Vol. 19, No.1, April 2008A Bulletin of the Indian Laser Association

Special Issue on Best Theses and Posters atNational Laser Symposium - 2007

Images from Best Thesis Presentations

ILA Executive Committee

PresidentP.D. Gupta, RRCAT, Indore

Vice PresidentV.K. Mago,BARC, Mumbai

Gen.Secy. IV.P.N. Nampoori,CUSAT, Kochi

Gen.Secy. IIS.V. Nakhe,RRCAT, Indore

TreasurerH.S. Vora,RRCAT, Indore

Regional RepresentativesR. Vijaya,IIT, MumbaiS. Pal,LASTEC, DelhiV. NatarajanIISc, BangaloreS. Khijwania,IIT,GuwahatiK. Das,CGCRI,Kolkata

Corporate RepresentativeLaser Spectra Services,Bangalore

Editor

L.M. Kukreja (RRCAT, Indore)

Editorial Board

K. Dasgupta (BARC, Mumbai)

P.K. Datta (IIT, Kharagpur)

S.P. Gaba (IRDE, Dehradun)

P.K. Gupta (RRCAT, Indore)

A.K. Nath (IIT, Kharagpur)

P. Radhakrishnan (CUSAT, Kochi)

H. Ramchandran (RRI, Bangalore)

P. Ramamurthy (University of Chennai)

G. Ravindrakumar (TIFR, Mumbai)

B.V.R. Tata (IGCAR, Kalpakkam)

R.K. Thareja (IIT, Kanpur)

K. Thyagrajan (IIT, Delhi)

Editorial Committee (RRCAT, Indore)

Rakesh Kaul Pankaj Misra

J. Jayabalan Tarun Sharma

V.S. Tiwari Rajiv Jain

A.K. Sharma P.K. Mukhopadhyay

H.S. Patel Sendhil Raja

Cover Photo :

Editorial Team of

Image on the top shows photograph of the diode end pumped single

frequency green laser at 532 nm operating with ~204 mW of output power

(Thesis of Jogy George). The laser was based on Nd:YVO /Brewster 4

plate/KTP configuration. The linewidth of the laser was ~17 MHz and the 2

output was nearly diffraction limited with M ~ 1.07. The optical-to-optical

conversion efficiency of the laser was ~33.7%, which seems to be one of the

highest reported values for such a system. Bottom image shows a composite

optical set up integrating multiple optical diagnostics for studying the

process of crystal growth (Thesis of Sunil Verma). It involves a

shadowgraphy technique for visualization of convective field during growth;

a Mach-Zehnder interferometer for measuring concentration and its

gradient; a Michelson interferometer for mapping surface microstructure and

a computerized tomography technique for obtaining 3D information of the

process parameters such as concentration and convection.

Page No.

From the Editor 1

Articles based on Best Theses presented at NLS-07

A study of Diode Pumped Solid State Lasers 2

Study of Ultra Cold Atoms in Maganetic and Optical Trap 7

Bose-Einstein Condensation in a Quasi-Electrostatic Trap 10

Development and Application of Optical Diagnostics for 17Imaging Crystal Growth from Solution

Articles based on Best Posters Presented at NLS-07

Comparison of the Properties of Microcrystalline TAG Powder 24Prepared by Sol-gel Techniques from Oxides and Nitrates

New Autoionization Resonances of Uranium by Three-color Resonance 27Ionization Spectroscopy in Hollow Cathode Discharge Tube

Effect of He-Ne Laser Irradiation on Hair Follicle Growth in Testosterone 31Treated Mice Investigated with Optical Coherence Tomography and Histology

Performance Characteristics of Remotely Tunable, High Repetition Rate, 35Copper Vapor Laser Pumped Single Longitudinal Mode Dye Laser

A Novel Technique of Intense keV X-ray Generation from in situ Laser 38Produced Silver Clusters

ILA Reports

Best Thesis and Best Poster Awards of National Laser Symposium - 07 42

thILA Short Courses Preceding 7 DAE-BRNS National laser Symposium 2007 43

Indian Laser Association (Receipt and Payment Account) 44

Report on National Laser Symposium-07 (NLS-07) 45

Announcements

ILA Lecture Scheme 47

ILA Membership Form 51

Vol. 19, No.1, April 2008

Contents

http://www.ila.org.in

In December 2007 DAE-BRNS National Laser Symposium (NLS-

07) was successfully organized at M. S. University of Baroda in Vadodara.

Like in previous years, the deliberations of the symposium included

presentations of theses and posters, which were evaluated and the best ones

were awarded by the Indian Laser Association (ILA). This issue of Kiran is

a compendium of the articles based on the award winning theses and

posters of NLS-07. While we congratulate the authors of these articles, we

also thank them for their efforts to write them in a short span of time.

During the NLS-07 a general body meeting of ILA was also held.

Amongst the deliberations of that meeting on the past and future activities

of ILA an idea was mooted that the members of ILA who volunteer to share

their expertise with and teach laser related areas to the students and faculty

at the colleges and universities in their vicinities could do so under the

umbrella of ILA. This is a worthy cause that needs to be promoted at the

earliest. This issue of Kiran has included details (please see on page 47)

about this recently introduced scheme of ILA. It is hoped that this scheme

will motivate the members of the Indian laser community to join the ILA's

efforts in extending the benefits of their knowledge and expertise to the

students and staff members in educational and research institutes of our

country.

Besides the aforesaid articles and details about the ILA lectures

scheme, in this issue we have included reports on the NLS-07, ILA web-

pages, ILA short courses preceding NLS-07 and a statement of its audited

account. I hope you will find this issue of 'Kiran' both interesting and

informative.

Lalit M. Kukreja

March 26, 2008

FROM THE EDITOR....

1

2

Single Longitudinal Mode (SLM) lasers

operate only in one of the allowed cavity modes.

They are used in wind velocity measurement,

LIDAR, high-resolution spectroscopy, coherent

optical communications, resonant cavity

doubling etc. A compact and efficient SLM laser

at 1064 nm may be realized in a diode end pumped

Nd:YVO laser based on a semi-monolithic type 4

of gain medium in a standing wave cavity.

However, certain applications demands single

frequency operation of the laser output. A single

frequency laser operating at a given wavelength

demands that it should oscillate in single

longitudinal mode (SLM), single transverse mode

(STM), and single polarization mode (SPM).

However, linearly polarized mode with 2

diffraction limited transverse beam profile (M

~1) would be preferred due its wider spectrum of

application than the other modes of operation.

The aim of the work presented in this thesis

was to study the diode pumped single frequency

laser generation in semi-monolithic Nd:YVO 4

gain medium and to extend its usefulness to other

wavelengths by harmonic generation (1064 nm /

532 nm / 266 nm). The work reported in this thesis

includes both experimental and theoretical

studies.

In our studies, we use semi-monolithic

crystals as the gain medium. These are gain

mediums, where a dichroic end mirror is directly

coated on one side of the crystal itself. The

dichroic end mirror provides high transmission at

the pump wavelength and high reflection at the

laser wavelength. These gain mediums are

beneficial for SLM operation. In addition, Stefen 1

et. al demonstrated that when the gain medium is

situated close to an end mirror, we could obtain

thermal lens insensitive resonator design by

choosing a resonator with g g of 1/2. The existing 1 2

definitions of resonator stability, either in terms of

g g formalism or (A+D)/2 formalism, provides 1 2

only a range over which the resonator is stable, but

does not discriminate any value in between. We

proposed new definition of stability, which

expresses the stability in a numerical scale

ranging from zero to 100%, with 100%

corresponding to g g of 1/2. The proposed 1 2

definition - the Degree of Optical Stability- was

characterized by the S parameter. The S parameter 2

was expressed in three different forms for

convenience as,

(1)

(2)

(3)

where, and S = 0 corresponds to

stable resonator, unstable resonator and

marginally stable resonator, respectively. Here, A,

B and D are the elements of round trip ABCD

matrix and Z is the Rayleigh in free space. We R0

also studied the S parameter for a plano concave

cavity with plane mirror acting as the output

coupler and gain medium kept very close to the

curved input coupler. We also measured the

misalignment tolerance of the cavity measured at

the plane output coupler and tried to correlate it

with the measured S parameter. The results are

shown in Fig.1. The measured value of S

parameter was closely matching with the

A Study of Diode Pumped Solid State Lasers

Fig. 1 : Measured S parameter using Eq. (3) and the

predicted S parameter using Eq. (1) along with the

measured value of the misalignment tolerance of a plano

concave cavity as a function of the cavity length.

Articles based on Best Theses presented at NLS-07

3

predicted values within the experimental error. In

addition, it was found that the misalignment

tolerance of the cavity was a maximum when S >

60%. Thus, we choose S > 60% in all our designs.

However, effort was also put to increase S

parameter closer to 100%, to have thermal lens

insensitive design. Keeping this in mind, we

started our study of the diode pumped single

frequency laser generation in semi-monolithic

Nd:YVO gain medium4

Two common techniques to achieve single

polarization mode (SPM) in a resonator is either

by inserting a Brewster plate inside the resonator

or by using a gain medium with inherent gain

anisotropy. The inherent gain anisotropy existing

in a-cut Nd:YVO laser was used in our designs to 4

get SPM operation. When an intracavity NLO

crystal such as type-II phase matched KTP crystal

is used for frequency doubling, the wave plate

action in KTP crystal can severely affect the SPM

operation. According to the theory of Helmfrid 3and Tatsuno , a-cut Nd:YVO /KTP laser support 4

SPM up to 28 times the laser threshold, as we

increase the pump power. To enhance the single

longitudinal mode (SLM) performance,

sometimes, an additional Brewster plate is also

inserted in between the KTP crystal and Nd:YVO 4

crystal. From our experimental studies, we found

that the insertion of the Brewster plate delays the

onset of the multi polarization significantly, and

SPM is supported in such a cavity up to 73 times

above the lasing threshold.

Two common techniques to achieve single

transverse mode (STM) operation in a resonator is

either by using a hard aperture or by using the

inherent gain aperture effect in an end pumped

gain medium. The transverse variation of gain

due to the spatial intensity profile of the laser

diode (pump source) generates soft aperture

effects in the resonator. This enables compact

laser design with diffraction limited laser output. 2

In a gain aperture governed system, the M 2parameter of the output laser beam M is related GA

to the spot-size ratio R as,pm

Here, k is the scale factor known to be unity for a

diffraction limited pump source. In the above

equation, W stands for the pump spot-size and p

w represent the TEM mode spot-size at the gm,00 00

gain medium. We use fiber coupled laser diodes

as the pump source, which have circularly

symmetric and nearly Gaussian type of spatial

intensity profile. However, they do not belong to

the category of diffraction limited and have 2M ~25. The value of the scale factor k is not

known from literature. Thus, we decided to

investigate the k parameter in an end pumped

resonator using a fiber coupled laser diode as the

pump source. It was found that when the spot-size

ratio R <1, the laser output was nearly diffraction pm

2limited with M < 1.5. However, as increased the

R >1, higher order transverse modes were pm

generated and this resulted in a quadratic variation 2of the M parameter. A least-square fit reveals that

best fit for the value of the k parameter was 0.98 +

0.02. Thus, k parameter is unity within the

experimental error. In fact, we adopted a novel

technique, i.e. the 2 spot method, to measure the 2

M parameter. Before using the technique, we

checked the accuracy of the method by

benchmarking it with a standard technique and

was found to be accurate (error was < 3%).

We also studied the effect of spherical

aberration of the beam transfer optics used to

transfer the pump beam to the laser medium. It 4was found that the existing model by Siegman

needed to be corrected to account for the larger

(4)

Fig. 2 : Predicted variation of the r parameter as a max

function of the axial mode separation in Nd:YVO laser. 4

The plot also shows the result of two experimental measurements. The validity of the existing HT model is also marked.

4

divergence of the fiber coupled laser diode. The 4existing model by Siegman was developed for

diffraction limited laser beams.

The filed of SLM operation of the semi-

monolithic Nd:YVO crystal at 1064 nm was 4

i n v e s t i g a t e d b o t h t h e o r e t i c a l l y a n d

experimentally. The SLM operation is understood

as due to the effective suppression of the spatial

hole burning effect, but up to a certain pump

power above the lasing threshold and is 3characterized by r parameter . In the theoretical max

3front, the existing model by Helmfrid et al.

(referred to as HT model) was extended to

overcome the shortcomings due to various 3assumptions involved. In fact, the HT model.

was derived for the special case, when

[A1] Dephasing is small within an absorption

depth

[A2] First oscillating mode is exactly at the line

center

[A3] Narrow band (frequency) pump is used for

optical pumping

Because of the assumption A1, the model

could not explain the observed enhancement in

the r -parameter with increase in the axial mode max

separation. Hence, the first task was to remove the

first assumption and re-derive the model. The

detailed derivations are presented in Appendix-A

of the thesis. The new model shows that r max

parameter does have a strong dependence on the 5axial mode separation . This was verified

experimentally. Fig.2 shows the results of the

measurement and the predicted variation of the

r parameter with the axial mode separation. The max

matching between the theory and experiment was

found to be very good.

The second task was to remove the

assumption A2 also. The new model correctly

predicts that SLM performance deteriorates

significantly (i.e. r parameter reduces) with max

shift in the location of the first mode away from 6the line center . The third task was to remove the

assumption A3, while retaining the other two.

This was done to simplify the results of the

analytical model. The detailed derivations are

presented in Appendix-B of the thesis. The new

model reveal that SLM performance deteriorates

when pump diode with multi-longitudinal mode

spectra with significantly high bandwidth is used

as compared to a narrow band pump tuned to the 7

absorption peak of the laser crystal .

All the above mentioned ideas were used to

develop diode end pumped single frequency

lasers at 1064 nm, 532 nm & SLM laser at 266 nm.

Compact single frequency IR laser at 1064 nm

To ensure SLM, an a-cut Nd:YVO crystal 4

with very strong absorption coefficient at the -1pump wavelength (~111 cm ) was used. A

compact plano concave cavity with ~6.7 mm

Fig. 3 : Photograph of the single frequency green laser at 532 nm operating with ~204 mW output power.

5

length and 75% stability (i.e. S parameter) was

used as the resonator. The active etalon effects in

the gain medium (Free Spectral Range, FSR ~129

GHz) enhanced the allowed range of SLM

operation. SLM operation was possible up to 5.62

times the threshold. The output power of the laser

was more than 100 mW. The output was linearly

polarized with more than 10,000:1 polarization

ratio. The spatial profile was a circular Gaussian

with 0.5% astigmatism. Gain aperture effect was

used to get diffraction limited laser output. The 2

measured M parameter was 0.99 + 0.08. The

RMS power fluctuation of the laser output was

~1% after a warm up to 30 min.

Highly efficient single frequency green laser at

532 nm

The usefulness of the single frequency laser

at 1064 nm was extended to 532 nm, by

intracavity frequency doubling using a 7 mm long

type-II phase matched KTP crystal. A folded V-

cavity with ~99.6% stability (both in sagital and

tangential direction) was used as the resonator.

The cavity consists of Nd:YVO /Brewster plate/ 4

KTP with the end mirrors directly attached to the

Nd:YVO and KTP crystal. Simultaneous use of 4

multiple effects ensured SLM operation. A 2 at-%

doped a-cut Nd:YVO gain medium with 72.4 4

-1cm pump absorption coefficient at 809 nm

provided short-absorption depth effects to

enhance SLM. The active etalon effects in the

gain medium with 66 GHz FSR in combination

with a birefringent filter of 250 GHz FSR ensured

SLM operation. Fig.3 shows the photograph of

the single frequency green laser at 532 nm

operating with ~204 mW output power. Fig.4

shows the SLM signature recorded using a sing a

scanning confocal spectrum analyzer with a

resolution of 7.5 MHz and FSR of1500 MHz.

Measurements revealed that the linewidth of the

532 nm laser was ~17 MHz. Polarization

measurements of the green output revealed that it

was linearly polarized with more than 100: 1 2polarization ratio. The M parameter measured at

532 nm was ~1.07. The system generated more

than 270 mW of single frequency green emission

with more than 33.7% optical-to-optical power

conversion efficiency from 809 nm to 532 nm.

This is the highest efficiency reported in the

literature, for a diode pumped single frequency

Nd: YVO / Brewster plate/ KTP laser at 532 nm.4

SLM laser at 266 nm by resonant doubling

The usefulness of the single frequency green

laser was further extended to ultraviolet (UV)

regime by intracavity doubling in a frequency

locked slave ring cavity using a 7 mm long b-

BBO crystal. Fig.5 shows the schematic of the

experimental setup. Hansch-Couillaud based

scheme was used for frequency locking. The

necessary negative feedback control electronics

was also developed for frequency locking. The

ring cavity was designed to have 100% stability in

the sagital direction and more than 94% stability

in the tangential direction. The transmission of the

input coupler chosen was 2.1% to ensure

impedance matching. The system generated more

than 3.4 mW of UV power at 266 nm at an incident

pump power of 225 mW at 532 nm.

Acknowledgements

The author is indebted to Prof. Bhanu P.

Singh (IIT Bombay) and Dr. S. C. Mehendale

(RRCAT, Indore) for their constant guidance

during the entire course of the work done reported

in this thesis. Timely support and co-operation of

members at the department of physics at IIT

Bombay and all members of Solid State Laser

Division are also thankfully acknowledged.

Fig. 4 : SLM signature of the single frequency green laser at 532 nm measured using a scanning confocal spectrum analyzer with a resolution of 7.5 MHz and free spectral range of 1500 MHz.

6

References

1. J. Steffen, J.P. Lortscher and G. Herziger, IEEE J.

Quantum Electron. 8, 239 (1972)

2. Jogy George, K. Ranganathan and T. P. S. Nathan,

Pramana J Phy. 68 (4), 571 (2007)

3. S. Helmfrid and K Tatsuno, J. Opt. Soc. Am. B 11,

436 (1994)

4. Siegman A E, Appl. Opt. 32, 5893 (1993)

5. Jogy George, Jolly X. P, S.C. Mehendale, B. P.

Singh, T.P.S. Nathan, , Opt Las Technol 39, 1193

(2007)

6. Jogy George and S M Oak, Proc. of DAE-BRNS

National Laser Symposium -07, vadodara, 37-38

(2007)

7. Jogy George and S M Oak, Proc. of DAE-BRNS

National Laser Symposium -07, vadodara, 35-36

(2007)

8. Jogy George, P K. Mukhopadhyay, V K Agnihotri stand T P S Nathan, ICOL-2005: 31 International

conference on optics and optoelectronis,

Dehradun, PP-lA-17 (2005)

9. Jogy George, V K Agnihotri, K Ranganathan, P K

Mukhopadhyay and T P S Nathan, PHOTONICS-

2004: Abstracts: OMD 5.5, page 332 (2004)

10. Jogy George and A K Nath, Full length paper:

NLO39, Abstract: PHOTONICS 2006 Abstracts,

Vol 2, p 367 (2006)

11. J o g y G e o rg e , K R a n g a n a t h a n , P K

Mukhopadhyay, S K Sharma, and T P S Nathan,,

Proc. of DAE BRNS National Laser Symposium,

Trivandrum, pp. 33-35 (2002)

12. Jogy George, V. K. Agnihotri, K. Antony, K.

Ranganathan, P. K. Mukhopadhyay and TPS

Nathan, Proc. of DAE BRNS National Laser

Symposium, Culcutta, Page 117, (2003)

13. Jogy George, V. K. Agnihotri, K. Ranganathan, P.

K. Mukhopadhyay & TPS Nathan, Proc. of DAE

BRNS National Laser Symposium, Culcutta,

Page-119 (2003)

14. Jogy George, Jolly Xavier P, V. K. Agnihotri and

TPS Nathan, Proc. of DAE BRNS National Laser

Symposium (NLS-4), Mumbai, pp. 158-160

(2005)

15. Jogy George, Manoj Saxena, V K Agnihotri, Jolly

Xavier P, and T P S Nathan, Proc. of DAE BRNS

National Laser Symposium (NLS-4), Mumbai,

pp. 161-163 (2005)

16. Jogy George, Renuka Sehgal and A K Nath , Proc.

of DAE BRNS National Laser Symposium (NLS-

6), Indore, pp. 45-46 (2006)

Jogy George

Solid State Laser Division,Raja Ramanna Centre for Advanced Technology,

Indore - 452 013.

Email : jogy@cat.ernet.in

Fig. 5 : Schematic of the experimental setup used to generate SLM UV laser at 266 nm by resonant cavity doubling technique.

7

The fundamental concept of laser cooling is derived from the momentum property of light as given by the de Broglie relation, and the notion that temperature is related to the kinetic energy and therefore to the velocity of an ensemble of particles. By using resonant or quasi-resonant exchanges of energy and momentum between atoms and laser light it is possible to obtain samples of atoms at temperatures in micro-Kelvin and even in nano-Kelvin range, where the atomic velocities range from a few cm/s to mm/s. Development of laser cooling techniques over the last few decades have made it possible to obtain unprecedented ultra-cold and very dense atomic samples of neutral atoms and that has opened up a rich new world of many exciting experiments and applications. This thesis comprises of development of experimental facilities for cooling and trapping of neutral atoms and study of atoms at ultra-cold temperature.

The starting point of any of the experiments and applications of ultra-cold atoms is a neutral

1atom trap that cools and confines atoms . Magneto-optical trap (MOT), which utilizes the light scattering force of an optical molasses combined with magneto-static confinement, is a forerunner of the neutral atom traps and has proven to be a workhorse for many of the laser cooling experiments. Despite the wide use of a MOT as a starting point in most of the exciting experiments including Bose Einstein condensate, Fermionic condensate, atom interferometry, ultra-precision measurements, ultra-cold plasma etc., the physical picture of a gas of laser cooled and trapped atoms inside a MOT is very complex, owing to the complexity of laser-atom coupling in multi-level atoms moving in a 3-D optical field and subjected to the effect of cold collisions. This thesis presents an in-depth study into the magneto-optic trapping of Cs and Rb atoms, and addresses to the fundamental issues of laser-atom and atom-atom interactions in the context of laser cooling and trapping of atoms. The realm of cold atoms is extended in the nano-Kelvin temperatures by the use of pure magnetic traps and optical dipole traps. The thesis presents some

initial experimental work done in this direction. The thesis is organized in eight chapters and the detailed investigations included in it are as discuss below:

Chapter-1 deals with the general introduction to the exciting world of laser cooling and trapping of atoms. The basic concepts and techniques are briefly described here with special emphasis on giving an intuitive description of the phenomena, rather than going in to the details of experimental configuration or chronology of the subject. The chapter is completed with the descr ip t ion of bas ic operat ional and phenomenological ideas behind some of the application of laser-cooled atoms, which have made a significant impact on contemporary science and technology. The contents of this chapter, thus, provide both the motivation and the basis for the work presented in the subsequent chapters.

Chapter-2 presents the investigations in high-resolution diode laser spectroscopy of atoms with a special reference to laser cooling and trapping of Rb and Cs atoms. One of the primary requirements in this work is the frequency stabilization of the external cavity tunable diode laser (ECDL) on or near of a Doppler-free atomic resonance. In this context, various configurations of the saturated absorption spectroscopy (SAS) are developed and the effect of external DC

2magnetic field and laser polarization on Doppler-free SAS spectrum is investigated in details. These experimental schemes are then used to accomplish frequency stabilization of ECDLs

3 4using both software and hardware locking strategies and also to demonstrate tunability of ECDLs under locked condition. In view of their importance in the diagnostics of laser-cooled atoms, the Doppler-free techniques of degenerate and nearly degenerate four wave mixing (DFWM and NDFWM) are extensively investigated in Cs

5atomic vapor . Our NDFWM experiments with

frequencies w=w +D (pump) and w+d (probe) 0

have revealed a new resonance at d=-2D besides

the usual resonances at d=0 and 2D, where w is 0

Study of Ultra Cold Atoms in Maganetic and Optical Trap

8

frequency of 6s F=4 ® 6p F¢=5 transition. This 1/2 3/2

new resonance is characterized for a wide range of pump frequency and its origin is explained in terms of the backward Bragg scattering of the forward pump. In a similar manner the experiments in DFWM in presence of a state-preparing laser have revealed additional new features, hitherto not reported in the literature. Details of this work with a special focus on the new findings are presented in Chapter-2.

Chapter-3 is devoted to the development of atom traps for Rb and Cs atoms. Central theme here is the design and development of MOTs for cooling and trapping of Rb and Cs atoms, and it includes various key experimental aspects such as ultra high vacuum optical chamber, optical lay out, generation of spherical quadrupole magnetic field and continuous metal vapour admittance system. Auxiliary experimental techniques developed for characterization of magnetic field gradient and density of background atoms by absorption spectroscopy are also discussed. All these issues are presented separately for MOTs for Rb and Cs atoms along with the protocols developed for obtaining cooled and trapped

1clouds of these atoms . These traps form the starting point of the research carried out in the present thesis. The chapter also contains initial work carried out towards development of a pure magnetic trap, QUIC trap, and a far off detuned dipole trap for Rb atoms using focused Yb:Yag laser.

The intrinsic characteristics of a cold cloud of atoms formed in a MOT are the steady state number of trapped atoms, their density, temperature and lifetime. These characteristics are dependent on the atom capture rate and the collision processes, which are in turn governed by the operating parameters of the trap. Characterization of the cooled and trapped atoms and their optimization is central to any experiment based on the cold atoms. A detailed account of the work carried out towards these objectives is presented in Chapter-4. It contains the development of specialized techniques of fluorescence and absorption imaging, and optimization of number of trapped atoms with respect to the background vapour density, magnetic field gradient, laser detuning and

trapping laser intensity. Time resolved fluorescence spectroscopy technique has been developed for investigations of trap filling curves and obtain the information on linear and quadratic

6collisional losses . During the course of this work a new and simple technique for measurement of temperature of the cold atoms has been developed 7. The technique has been compared with the known technique of release and recapture, and has been further used to establish the temperature scaling law for a MOT. The chapter also contains details of the observation of multiple cloud structures in a MOT; an observation hitherto unreported.

Chapter-5 is devoted to our observation of a new phenomenon of enhancement in the number of trapped atoms in a MOT by a near-resonant

8control laser beam . In this work we demonstrate enhancement in the number of trapped cesium atoms in a magneto-optical trap using a control laser that illuminates only a fraction of the capture region of the trap without interacting with the cold cloud of atoms. The enhancement is observed to maximize when the laser is slightly blue-detuned (~ 5 MHz) with respect to the cooling transition. The kinetics of this phenomenon is studied in detail using MOT loading curves and their analysis. Trap loading curves obtained under the modulation of the cooling lasers point to ~ 2 fold increase in the capture rate, which as a consequence results in the increase in the steady state number of trapped atoms. Enhanced loading is further confirmed by MOT loading and decay curves obtained under the modulation of the control laser beam. Based on the experimental observations the optical pumping of the inaccessible Zeeman states into the stretched states is suggested as a possible mechanism. The details of this work, which provides a simple and interesting technique for increased efficiency in a MOT loading, are presented in this chapter.

In Chapter-6 we develop a new experimental configuration and related concepts for optical

9control of a MOT based on the generalizations of observations and ideas built in chapter-5. We show here that a control laser beam added to a Cs

MOT and tuned over the 6s F=4 ® 6p 1/2 3/2

F¢=3,4,5 hyperfine manifold provides a scheme

9

for controlling the number of cooled and trapped atoms. Systematic investigations reveal that this control is enabled by the interplay of two distinct position dependent processes in a MOT, one responsible for enhancement and other for depletion. While enhancement occurs due to optical pumping, the depletion is shown to arise from heating of the cloud resulting in expulsion of cold atoms. These two processes are shown to combine to produce a general variation in the number of trapped atoms, which can be controlled by the position, intensity and frequency of the control beam. The ability to vary the number of trapped atoms without changing the MOT operating conditions makes this study interesting and potentially useful for controlling the number of trapped atoms necessary for various experiments in quantum optics and collision physics.

In Chapter-7 we report a study on the expansion of a cold atomic cloud in the presence

10of a near resonant laser field . The problem is examined using a simple experimental system where a cold cloud of Cs atoms formed in a MOT is allowed to expand in 1-D in presence of 2-D configuration of near resonant beams that are orthogonal to the expansion direction. Experimental results are analyzed using a stochastic model based on Langevin equation. We demonstrate that such a cloud expansion exhibits three distinct features in different time domains- initial contraction followed by ballistic expansion and eventually super-ballistic explosive expansion at long times. Sudden initial contraction of the cloud observed in our experiments provides a direct evidence for the existence of the radiative trapping force in the MOT and extent of contraction is found to be consistent with the Sesko-Walker-Wieman model. In the intermediate time scale we show that the cloud expands essentially in the ballistic manner as determined by the initial temperature of the cloud. In the third time domain, the ballistic expansion is overtaken by the stochastic heating of the cloud arising from the fluctuations of the trapping force. Analytical expressions obtained from the Langevin formulation of the problem are used to obtain velocity diffusion coefficient from the experimental data. Observed diffusion

coefficient is found to correlate well with the diffusion coefficient of the MOT. The experimental and theoretical studies presented in this chapter, thus, provide a fresh insight into the issue of the motion of atoms in near-resonant radiation field.

Finally the Chapter-8 of the thesis comprises of the important conclusions and future scope of the work.

References

1. S.Pradhan, A.P.Marathe, S.J. Gaur, A. Venugopalan, K.G. Manohar, and B.N. Jagatap, Ind. J. Phys. 76B, 545 (2002).

2. A. Ray, S. Pradhan, and B.N. Jagatap, Asian J. Phys. 16, 4 (2007).

3. S. Pradhan, S.J. Gaur, V.S. Rawat, K.G. Manohar, and B.N. Jagatap, Recent Advances in Atomic and Molecular Physics: Ed. Rajesh Srivastava, Phoenix, India, pp. 296- (2001).

4. S.J. Gaur, S. Pradhan, K.G. Manohar, and B.N. Jagatap, Ind. J. Phys. 76B, 537 (2002).

5. S. Pradhan, and B.N. Jagatap, “Resonances in degenerate and near degenerate four-wave mixing”, (To be communicated)

6. S. Pradhan, S.J. Gaur, K.G. Manohar, and B.N. Jagatap, Bulletin of Indian vacuum society, 8, 27 (2005).

7. S.Pradhan, and B.N. Jagatap, Rev. Sc. Instru. 79, 013101 (2008).

8. S.Pradhan, S.J. Gaur, K.G. Manohar and B.N. Jagatap, Phys. Rev. A 72, 053407 (2005).

9. S.Pradhan, and B.N. Jagatap, J. Phys. CS 80, 012041 (2007).

10. S.Pradhan, Y.S. Mayya, and B.N. Jagatap, Phys. Rev. A, 76, 033407 (2007).

S. PradhanLaser and Plasma Technology Division,

Bhabha Atomic Research Centre, Mumbai - 400 085.

E-mail : spradhan@barc.gov.in

10

Bose-Einstein condensation (BEC) was predicted in 1925 when Einstein implemented the

1work of Satyendranath Bose on photon statistics for the case of bosonic particles to predict macroscopic occupation of the lowest energy state at finite temperature even without

2interaction . Bose-Einstein condensation happens when the average inter-particle separation becomes smaller than the thermal de Broglie

wavelength l . Characteristics of Bose-Einstein dB

condensation was first identified in strongly interacting systems e.g. superfluidity in Helium-4 (1938).

BEC in a dilute atomic vapor of weakly-3,4,5

interacting atoms was first observed in 1995 . This enabled the detailed study of the macroscopic quantum state in absence of strong interactions, which makes the system closely resembling the original prediction of condensation in non-interacting systems. Since then the experimental and theoretical work on BEC has progressed with a remarkable pace and has generated a lot of interest and impact in the scientific community. The rich physics of quantum fluids and the successful observation of the phenomenon of Bose-Einstein Condensation (BEC) in cold atomic vapors were the main motivation for awarding two sets of Nobel prizes in Physics in 1997, and 2001. Since 1995, the research on BEC has seen a wide expansion, and has led to major improvements of our understanding of the behavior of highly degenerate Bose and Fermi gases at very low

6,7temperatures .

From an experimentalist’s point of view the BEC is a small cloud of gas in a very special state in the sense that all the atoms constituting the state are coherent and share the same wave-function. In the last decade, many interesting experiments have utilized this property of BEC to explore the properties of coherent matter waves e.g.

8interference between two BECs , the collective behavior in BEC such as the excitation of

9collective modes , observation of vortices in

10rotating Bose condensate , observation of Hanbury-Brown Twiss effect using matter

11waves etc. The field contributed significantly to the understanding of the phenomenon of superfluidity in the context of dilute degenerate gases. Recent research using cold fermions to investigate the nature of BEC-BCS crossover regime is promising for a better understanding of

12high T superconductivity . c

The research related to BEC in atomic vapor is no more bound to just atomic physics but has generated high level of interest in other fields such as condensed matter physics. BEC and cold atoms have also become valuable tools for precision measurements. For example, weak short range forces due to atom-surface interaction such as Casimir-Polder and Van-der Waals forces were

13measured with high precision using BEC and

14cold atoms . Since the kinetic energy of the atoms are negligibly small at or close to the BEC phase, the experiments using ultra-cold atoms and BEC allow more than thousand times increase in the observation time and hence enhance the precision in measurement of weak fundamental forces. The same advantage as well as the weak mutual interaction has enabled the realization of ultra-stable clocks using cold atoms.

BEC and cold atoms in Optical lattices have opened up another vibrant field of research. Tunability of the lattice parameters as well as of the occupation of lattice sites enables ideal simulation of quantum mechanical condensed matter systems. Observation of Superfluid-Mott

15insulator transition is one such example.

This thesis is on the production of an All-87

Optical Bose-Einstein condensate (BEC) of Rb atoms in a Quasi-Electrostatic trap. Most of the Bose-Einstein condensates in the world are produced in magnetic traps which can trap only one or two of the spin states. In optical dipole traps, this limitation of magnetic traps is circumvented where atoms in all spin states or in general in a superposition of different spin states can be trapped. This advantage in Optical Dipole traps enables the study of interesting spin dynamics in all-optical Bose-Einstein condensates. Moreover, optical traps provide

Bose-Einstein Condensation in a Quasi-Electrostatic Trap

11

flexibility in trap design which in turn allows use of BEC as a tool for various studies such as simulation of condensed matter systems using BEC loaded in Optical lattices, Cavity QED effects, probing short range forces such as Casimir-Polder force etc.

The first BEC in a purely optical trap was produced in the year 2001 in Georgia Institute of

16Technology . Since then there have been very few successful production of BEC in optical dipole

1 7traps . For producing a Bose-Einstein Condensate in both magnetic and optical dipole

18traps, evaporative cooling is the key technique to cool atoms to sub-micro-Kelvin temperatures to reach the critical temperature for BEC phase transition in weakly interacting dilute gases. Evaporative cooling technique is based on removal of higher energy atoms from the trap which causes loss of atoms from the trap. Hence it is desirable to start from a large number of atoms at the very outset to have the largest possible number of atoms in the BEC phase. To fulfill this objective of having a larger initial number of

10atoms, an atomic beam with a high flux of 2 × 10

19atoms/sec was produced to load the magneto-optical trap (MOT) which can load 1000 times

10more atom in a MOT (10 atoms in our experiments) within 500 ms as compared to the

7most common Magneto-optical traps (10 atoms) which are loaded from the background vapor of atoms in 20-30 seconds. Hence a large number of atoms could be loaded from this pre-cooled atomic cloud in MOT into the Optical Dipole trap

7(more than 1 × 10 atoms in this case) which is several times larger than other similar

16,17 5 experiments . Bose-Einstein Condensate of 1087Rb atoms was produced in the Optical dipole trap after forced evaporative cooling for about 1 second. An important signature of Bose-Einstein Condensation was obtained by observing the anisotropic expansion of BEC released from an anisotropic trap which establishes a clear distinction from a thermal cloud which expands isotropically independent of the trap configuration.

Cooling, Trapping and Manipulation of atoms

The first experimental step for any BEC experiment is laser cooling and trapping of neutral

21atoms . Since the velocities of the atoms in a room temperature vapor (300 K) is of the order of several hundred m/sec and at BEC phase t r a n s i t i o n t e m p e r a t u r e ( 3 0 0 n K , f o r experimentally achievable densities) it is only a few mm/sec, it is evident that the momentum of the atoms need to be reduced by several orders of magnitudes. It is not possible to have such a huge reduction in temperature in a single step. Laser cooling and trapping techniques developed by late 1980’s are of extreme importance to reduce the velocities of atoms to a few cm/sec. Though it is not possible to reach BEC by laser cooling alone because of various temperature and density limiting processes such as single-photon recoil

22,23limit, photon re-scattering , hyperfine changing

24collisional losses , it is important to have a pre-cooled sample of cold atoms around 100µK temperature, and at atom number density close to

11 310 atoms/cm , which can be achieved by laser cooling techniques in a Magneto Optical Trap (MOT), before proceeding towards producing BEC by loading this pre-cooled sample of atoms in dark traps like magnetic or optical traps where there is absence of scattering and heating from near-resonant light. The phase space density in a

-7MOT is less than 10 , and this indicates the need for implementing several carefully designed and executed steps to reach a phase space density exceeding unity.

+A 2D MOT source of cold atomic beam with high flux

A source of a slow, intense, and collimated beam of rubidium atoms with high flux was

+Fig. 1 : Experimental set-up for producing the 2D MOT and the 3D-MOT loaded from the high

+flux cold atomic beam from the 2D MOT.

12

19produced by two-dimensional magneto-optical trapping in directions transverse to the atomic beam axis and unbalanced Doppler cooling in the axial direction. The novel design allows use of relatively low laser power and a considerably simplified assembly.

The atomic beam has a high flux of about 10

2×10 atoms/s at a total cooling laser power of only 55 mW. It has a narrow longitudinal velocity distribution with mean velocity of 15 m/ s with full width at half maximum 3.5 m/ s and has a low divergence of 26 mrad. The high flux enables

10ultra-fast loading of about 10 atoms into a 3D magneto-optical trap within 500 ms (Fig. 2). The variation of atomic beam flux was studied as a function of cooling laser power, transverse cooling laser beam length, detuning of the cooling laser, and relative intensities of the cooling beams along the atomic beam axis in order to keep these parameters in optimized condition during the experiment. A detailed comparison of our measurements of the cold atomic beam with a 3D numerical simulation was also done.

Ultra-fast Loading of large atom number in a 3D-MOT

+ The atoms from the 2D MOT cold atomic

beam were loaded into a large 3D-MOT in the main experimental chamber. The high flux of

+atoms in the beam produced by the 2D MOT with their velocity smaller than the capture velocity of 3D-MOT results in ultra-fast loading of the MOT with high number density. Within 500 ms,

101.2×10 atoms are loaded into a 3D MOT (Fig. 2) of size 5 mm as measured from the fluorescence collected in the calibrated detector. This loading rate is about 100 times faster compared to what is typically possible in the most commonly used double-MOT systems. It is a significant advantage to reduce the atom loading time for subsequent experiment e.g., to proceed to produce BEC by evaporative cooling. Apart from the advantage of increasing the repetition rate of the experiment, the fast loading allows us to capture the maximum possible number of atoms in the MOT since the loading rate is much higher than the trap loss rates due to collisions with background atoms.

Temporal dark MOT technique to enhance phase-space density in the MOT

For optimized loading of atoms into the dipole trap, there is a requirement of reduction of temperature of the trapped atoms along with the enhancement of the atom number density. This is achieved by using a combination of sub-Doppler cooling and the temporal dark MOT technique. The atom number density obtained in our 3D-

11 3MOT is about 1.5 × 10 atoms/cm . This is at the limit of the density possible in the magneto-optical trap because of the photon re-scattering process which is particularly significant in high density magneto-optical traps as in our experiment. Hence it is absolutely essential to reduce the photon re-scattering. After loading atoms in the MOT they are optically pumped to the lower hyperfine ground state (dark state) to reduce density limiting processes such as photon re-scattering. Also cooling laser detuning was increased along with the reduction of intensity to enable efficient sub-Doppler cooling. The efficiency of transfer of atoms to the dark state was measured to be more than 95 percent. This technique is referred to as temporal dark MOT technique. After the temporal dark MOT phase, the atomic cloud is compressed and the atom number density is increased by a factor of 40 at the centre of the magneto-optical trap. The dipole trap was kept on at full power throughout the MOT loading and temporal dark MOT phase. The criteria for optimization of the various parameters for the temporal dark MOT phase were to obtain the maximum transfer of atoms to the dipole trap.

Loading of atoms in a crossed Quasi-Electrostatic trap

Cold Rubidium atoms from dark-MOT were trapped and cooled in an optical dipole trap

Fig. 2 : Fast loading of 3D- MOT from the +cold atomic beam produced from the 2D MOT.

13

formed by two focused CO laser beams (l= 2

10.6mm) with 18 Watts power in each beam, crossing at the focal point orthogonally (Fig. 3) at the magneto-optical trap centre. The near

resonant (l=0.78 mm) cooling laser beams and the magnetic field of the MOT were switched-off after atoms were loaded into the dipole trap. Since, the wavelength of CO laser is too far red-2

detuned from resonance with respect to any of the 87atomic transition of Rb, the atoms ‘see’ the light

field as almost an electrostatic field, hence the 20name “Quasi-Electrostatic trap” (QUEST) . The

3photon scattering rate is only one per 10 seconds, which makes it an ideal conservative trap. The trapping potential is created because of the spatially varying ac-stark shift. The trap depth is given by,

Where, a is the atomic polarizability, P is the trapping laser power and w is the waist of the 0

trapping beam at focus. In our experiment the trap 7

depth is around 350 mK. More than 1 × 10 atoms

at a temperature below 30 mK were efficiently 14 trapped in the QUEST with densities close to 10

3atoms/cm , ensuring an initial phase space density -3

larger than 10 .

A further reduction of the temperature was

measured in the dipole trap to about 14 mK within a second by spontaneous evaporation (Fig. 4). The fast reduction of temperature within the first 1 second is due to plain evaporation of atoms from the trap. The saturation of the final temperature at

14 mK well above the nano-Kelvin regime manifests the requirement for forced evaporative cooling to reach the BEC phase transition.

The vibrational frequencies in the dipole trap were measured using the parametric

25,26resonance method . At full power, the trap frequency for the crossed trap is 1.3 kHz along the tight trapping direction. Since the rate of evaporation depends on the trap frequency and the density of the atoms in the trap, these are important parameters that determine the efficiency of the evaporative cooling.

The detection of atoms in the experiment was mainly done using absorption imaging technique, where a weak resonant probe beam of circular cross-section was pulsed for duration of 100 micro-seconds after releasing the atoms from the trap allowing the atom cloud to expand ballistically for a variable time. The shadow cast by the atoms in the probe beam was imaged onto an EMCCD camera. The number of atoms is measured by integrating the total optical density in the absorption image, and the temperature of the thermal cloud is measured by observing the size of the cloud at various expansion times.

Bose-Einstein Condensate in a Quasi-Electrostatic trap

After an initial trapping time of 50 msecs in the trap, forced evaporative cooling was done by reducing the intensity of the trapping beam using accousto-optic modulators.

Forced evaporative cooling is the most efficient technique to cool atoms in dark traps like magnetic traps or optical dipole traps to sub-microKelvin temperatures. Evaporative cooling is based on the removal of the most energetic atoms from the trap which is followed by a re-Fig. 3 : Absorption image of atoms trapped in the

crossed dipole trap: (a) side-view, (b) top-view.

Fig. 4 : Temperature reduction due to spontaneous

evaporation of atoms in the optical dipole trap.

14

thermalization of the remaining atoms by elastic collisions resulting in the reduction of the overall temperature of the system. The great potential of evaporative cooling technique is evident from the fact that it can increase the phase-space density of the atomic cloud by six orders of magnitude. For efficient evaporative cooling, it is important to have a large ratio between the elastic collisions and the inelastic collisions since elastic collisions enable thermalization and lowering of temperature by evaporation whereas inelastic collisions causes loss of atoms from the trap along with heating due to inelastic energy exchange between atoms. The inelastic collisions include collisions with the background gas and three-body recombination.

The requirement for reaching the BEC phase transition is the phase space density,

Where, l is the thermal de Broglie dB

wavelength of the atoms and n is the atom number density. In other words the atomic wave-functions overlap to form a macroscopic wave-function. This translates to the equation for the critical temperature (T ) for phase transition,c

Where, w is the mean trap frequency and N is the number of atoms in the condensate phase. In

5our experiments, for 10 atoms the BEC transition

temperature is about 300 nK. The atomic cloud in the trap was evaporatively cooled down to 140 nK (Fig. 5), well below the BEC transition temperature. During the forced evaporative cooling, the atom number density in the trap also increases along with the reduction in temperature resulting in the final phase-space density of 20 which is well above the requirement of 2.612 for reaching the BEC phase transition.

Even though the ground state wave function in a harmonic potential is a Gaussian, because of the presence of weak repulsive interaction between the atoms, the ground state wave function takes the shape of the trap. The evidence for Bose-Einstein condensate is obtained by fitting thermal Bose-Einstein distribution function to the wings of the density profile of the absorption image of the evaporated cloud at different stages of evaporation as shown in Figure. 6. It is observed that when the condensate starts forming, the density profile at the centre is enhanced beyond the thermal Bose-Einstein distribution. This is a signature of the Bose-Einstein condensate phase in the harmonic trap. The enhancement is highest after evaporation to a final trapping power of 210 mW.

The expansion of BEC is governed by the release of mean field energy due to the weak repulsive mean-field interaction between the atoms in the condensate. Thermal, incoherent gas released from trap expands to an isotropic shape asymptotically in time, independent of the shape

Fig. 5 : Temperature reduction due to forced evaporative

cooling in dipole trap. The forced evaporative cooling of

the atoms progresses efficiently to cool the atoms in the

crossed dipole trap to 140 nano-Kelvin temperature.

Fig. 6 : Density profile of evaporated atomic cloud at

various stages of evaporation depicting deviation from

thermal distribution towards the end of evaporation

process indicating the BEC phase transition

15

of the confining potential since the mean square velocity is isotropic for the thermal gas. In case of BEC released from an anisotropic trap the expansion is faster in the direction of tighter confinement due to the anisotropic release of mean-field energy, which reflects the anisotropy of the confining potential since all the atoms in the BEC follow the same wave-function. This anisotropic expansion of the BEC results in the reversal of the aspect ratio after a certain duration of expansion. After producing the BEC in an isotropic crossed trap, the BEC was transferred to an anisotropic single beam optical trap. After holding the BEC in the anisotropic trap for 20 ms, the dipole trap was released and the atomic cloud was observed using absorption imaging at different durations of expansion. The reversal of aspect ratio of the Bose-Einstein condensate was observed after 6 ms of free expansion as shown in Fig. 7. Thermal, incoherent gas expands isotropically, whereas in case of BEC released from an anisotropic trap the expansion is faster in the direction of tighter confinement. For comparison, a thermal cloud was also released from the trap and absorption images were taken after various expansion times. The different characteristics of expansion of a BEC and a thermal cloud is evident from the data in Fig. 9 where the aspect ratio of the thermal cloud is observed to be asymptotically reaching the value of 1 for longer expansion times whereas the aspect

ratio of BEC crosses the value of 1 after 6ms of expansion and reaches well above 1 for longer expansion times resulting in inversion of aspect ratio of the BEC which manifests the significant role of mean-field interaction between the atoms in the BEC state. This anisotropic expansion is an important & unambiguous signature of the BEC.

Conclusion and Outlook

87A Bose-Einstein condensate of Rb atoms was produced in a Quasi-Electrostatic trap formed by tightly focusing two high power CO laser 2

beams in orthogonal directions. To start with a high initial atom number in the magneto-optical

+trap, a 2D MOT source of cold atomic beam was built which could produce cold atoms with a high

10flux of 2×10 atoms/sec loading into a 3D-MOT 10

to a large atom number of 10 within 500 msecs. The atom number density in the 3D-MOT was

11 about 1.5×10 atoms/cc. Sub-Doppler cooling and temporal dark MOT techniques were implemented to enhance the atom number density

12 7 further to about 5×10 atom/cc. More than 1×10atoms could be loaded into the crossed optical

87dipole trap. Bose-Einstein Condensate of Rb atoms was produced in the Optical dipole trap after forced evaporative cooling for about 1

27second . The technical simplicity of our experimental set-up combined with its advantages of exceptionally high atom number and density in the MOT enabled a very high initial atom number and a high evaporative cooling speed in the dipole trap, making it a convenient and versatile set-up for experiments with ultra-cold atoms and BEC.

The design of the 3D-MOT is indeed an ideal starting point for magnetic trap BECs as well due to the large number of atoms and fast loading. BEC and cold atoms are extremely useful tools to investigate fundamental physics issues as elaborated in the introduction. Innovative design aspects implemented during this work tested successfully a strategy that ensured reliable production of the BEC with relatively large number of atoms in short evaporation duration.

BEC produced in an optical trap offers several advantages for studying spin dynamics. After producing BEC in crossed Optical Trap, we

Fig. 7 : Inversion of aspect ratio due to anisotropic expansion of the BEC. The open circles and the dots correspond to the data for BEC and the thermal cloud, respectively. The nature of expansion of BEC from an anisotropic trap differs remarkably from that of a thermal cloud due the role of mean-field interaction between atoms in the BEC state.

16

have trapped atoms in a 1D Optical lattice created by making spatial interference pattern in one of the trapping light beams. Evaporative cooling in the Optical lattice is done to produce BEC directly in a lattice. Since the research with BEC and cold atoms have reached a stage where its impact and use extends to several areas of fundamental physics and applications, the work carried out and described in this thesis enables us to explore fundamental physics of quantum degenerate gases.

Acknowledgements

The author is grateful to his PhD thesis supervisor Prof. C. S. Unnikrishnan and colleague Sanjukta Roy for their valuable guidance and support during this thesis work.

References

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4. K. B. Davis, M. O. Mewes, M. R. Andrews, N. J. van Druten, D. S. Durfee, D. M. Kurn, and W. Ketterle, Phys. Rev. Lett. 75, 3969 (1995).

5. C. C. Bradley, C. A. Sackett, J. J. Tollett, and R. J. Hulet, , Phys. Rev. Lett. 75, 1687 (1995).

6. Bose-Einstein Condensation in Dilute Gases, C. J. Pethick and H. Smith, Cambridge University Press (2002).

7. Bose-Einstein Condensation, Lev Pitaevskii and Sandro Stringari, Oxford Science Publications (2003).

8. M. R. Andrews, C. G. Townsend, H.-J. Miesner, D. S. Durfee, D. M. Kurn, and W. Ketterle, Science 275, 637 (1997).

9. D. S. Jin, J. R. Ensher, M. R. Matthews, C. E. Wieman, and E. A. Cornell, Phys. Rev. Lett. 77, 420 (1996)

10. J. R. Abo-Shaeer, C. Raman, J. M. Vogels, W. Ketterle, Science 476, 292 (2001)

11. M. Schellekens, R. Hoppeler, A. Perrin, J. Viana Gomes, D. Boiron, A. Aspect and C. I.

Westbrook, Science 310 648 (2005)

12. M. W. Zwierlein, J. R. Abo-Shaeer, A. Schirotzek, C. H. Schunck and W. Ketterle, Nature, 435 (2005)

13. D. M. Harber, J. M. Obrecht, J. M. McGuirk, and E. A. Cornell, Phys. Rev. A 72, 033610 (2005)

14. A. K. Mohapatra, S. Chaudhuri, S. Roy, C. S. Unnikrishnan, Eur. Phys. J. D 42, 287–298 (2007).

15. Markus Greiner, Olaf Mandel, Tilman Esslinger, Theodor W. H¨ansch and Immanuel Bloch, Nature 415, 39 (2001)

16. M. D. Barett, J. A. Sauer and M. S. Chapman Phys. Rev. Lett. 87 010404 (2001)

17. G. Cennini, G. Ritt, C. Geckeler and M. Weitz Appl. Phys. B 77, 773-779 (2003).

18. F. H. Harald Phys. Rev. B 34 3476 (1986)

19. Saptarishi Chaudhuri , Sanjukta Roy , and C. S. Unnikrishnan Phys. Rev. A 74, 023406 (2006)

20. R. Grimm, M. Weidmüller, and Y. B. Ovchinnikov, Adv. At., Mol., Opt. Phys. 42, 95 (2000)

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Saptarishi ChaudhuriDepartment of High Energy Physics

Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba,

Mumbai - 400 005.E-mail: wrishi@tifr.res.in

17

Crystals are the workhorses driving the

current photonics revolution. Material scientists

need to have a detailed understanding of how

crystals grow, whereas device engineers need to

grow large relatively defect-free crystals that are

adequate for the end applications. The process of

mass transfer and the convection modes adopted

to achieve the desired mass transport rates during

growth present a difficult optimization problem.

The transport process affects the growth rate,

crystal quality and the surface microstructure of

the growing crystal faces. As a result the science

of crystal growth is governed by the principles of

physico-chemical hydrodynamics during fluid-

to-solid phase transition. Therefore, in order to

control the process and to ensure growth of high-

quality crystals, it is important to understand the

physical phenomena involved during growth.

The present thesis concerns the study of the

process of crystal growth from solution. Since the

change of solution density with temperature

(dr/dT) is negative and that with solute

concentration (dr/dC) is positive, thus the growth

in the gravitational field is often accompanied by

a rising buoyant convection current. This

envelops the crystal, is oscillatory and unstable,

and drastically modifies the concentration

gradient along the growth interface. As a result the

growth history and defect structure of the crystal

is a function of the time-dependent spatial

distribution of the convection patterns and of the

concentration profiles in the surrounding

solution. Therefore, mapping of these two

parameters during growth is a useful experimental

approach to understanding the process of crystal

growth and regulating growth conditions to

produce crystals of optimal quality.

In the work reported here, convection,

concentration and surface features have been

imaged during growth of a KDP (Potassium

Dihydrogen Phosphate) crystal. The relationship

of the process parameters to the growth rate,

crystal quality and growth mechanism is studied.

KDP crystal has been chosen for study as it is an

important NLO material and its growth related

physico-chemical properties are available in the

literature. Due to several advantages offered by

the optical techniques, they have been employed

in the present work. They correspond to photon

probes that do not perceptibly affect the process

being studied and their response is practically

inertia-free. They map the convection and

concentration field with a spatial resolution of a

micrometer and a temporal resolution of about a

millisecond. In addition they are capable of

providing a large volume of data of the process

under study. The salient results of our work are

reported below:

Apparatus and Instrumentation

In order to perform the above reported

studies, several optical diagnostics and opto-

mechanical instruments have been designed and

fabricated. These include a shadowgraph optical

diagnostic for convection mapping, a rigid-type

constant-deviation Mach-Zehnder interferometer

for concentration measurements, a Michelson

interferometer for surface structure analysis, a

double-Mach-Zehnder interferometer for

simultaneous measurement of the flow and

surface features, computerized tomographic

imaging set up, and finally a composite optical set

up integrating all these techniques (Figure 1). For

tomography experiments a wedge-compensator

based multi-window chamber & a high-precision

wobble-free motorized platform were also

designed and fabricated {Figure 2(a-c)}. Specific

instrumentation for the image acquisition and

processing was also set up. The ariel view of the

imaging set up is shown in Figure 3.

Shadowgraph Imaging of Convection during

Growth

Laser shadowgraph technique has been used

for mapping free convection phenomenon during

Development and Application of Optical Diagnostics for Imaging Crystal Growth from Solution

18

Fig. 1 : Optical schematic of the composite experimental set up integrating multiple optical diagnostics.

Fig. 2 : Eight-window crystal growth chamber. (a) Top view of the cell, (b) side view of the chamber with crystal hanging assembly, and (c) chamber placed on a motorized rotation & translation assembly.

(a) (b) (c)

Fig. 3 : Shadowgraphy, interferometry (Mach-Zehnder and Michelson) and tomography experimental set up.

19

growth in three different geometries (Figure 4).

Our results bring out the importance of gravity in

the crystal growth process. The convective

activity is observed to make transition from being

laminar to chaotic, which has a bearing on the

quality of the growing crystal. The influence of

free and forced convection, and the cooling rate

on the growth rate and the quality of the grown

KDP crystal has been studied. The strength of free

convection observed through shadowgraph

images is estimated in terms of Grashof number. It

is observed that beyond a given supercooling the

Grashof number rises exponentially (Figure 5a),

and the crystal quality becomes sensitive to

fluctuation in the concentration field. This critical

Grashof (Rayleigh) number falls within 60 to 85 4(~3×10 ). Inclusions and striations get

incorporated beyond this stage of growth. The

time-lapsed shadowgraph images are used to

quantify the growth rate as a function of

supercooling (Figure 5b). The shadowgraph

images of convective plumes during free

convection growth have been used to examine

growth mechanisms. The signatures of two new

growth mechanisms, namely “layer-by-layer

growth” and “3D cluster growth” at high levels of

supersaturation have been identified. At this stage

the growth rate along a-b directions increases

several folds. The thickness of the solutal

boundary layer (SBL) has been imaged and

measured precisely for different habit faces of the

crystal. It lies in the range ~150-300 mm. It has

been found to be intricately linked to the growth

kinetics. Thinner the boundary layer, faster is the

growth kinetics. A linearized governing equation

of the shadowgraph process has been obtained to

extract refractive index field corresponding to the

shadowgraph image (Figure 6). This information

is used to trace the optical rays through the growth

chamber. The results suggest that the higher order

optical effects such as scattering and interference

are insignificant during shadowgraph imaging,

as the ray deviations are consistently small

(Figure 7).

Mach-Zehnder Interferometric Imaging

A novel design constant-deviation Mach-

Zehnder interferometer has been fabricated and

installed for imaging concentration field during

KDP growth under free and forced convection

conditions. The design of the interferometer is

such that it is immune to frequent misalignments

Fig. 4 : Free convection activity during KDP crystal growth in different geometries.

Fig. 5 : (a) Variation of Grashof number as a function of supercooling and crystal characteristic length. Beyond a given supercooling the Grashof number increases exponentially. (b) Growth rates as a function of supercooling along <100> & <001> crystallographic directions of KDP crystal.

20

due to external vibrations and ambient

temperature fluctuations. Imaging of the

concentration field during growth in the top

hanging geometry has been carried out for various

forced convection conditions {Figures 8(a-d)}.

These are achieved by varying the rotation rate

and the time periods of the acceleration and

deceleration phases of a rotation cycle. Results

indicate that a uniform concentration is achieved

only at a given value of these parameters. These

correspond to an average Reynolds number of

1600 for the top hanging growth geometry and

7100 for the platform growth geometry. Infinite

fringe M-Z interferometry is demonstrated to be

an extremely sensitive diagnostic tool to detect

and quantify the solution stratification during free

convection growth {Figure 9(a-f)}. Stratification

is a limiting factor for growth under free

convection at high cooling rates and for long

durations.

Tomographic Reconstruction of Convective

Features using Shadowgraph Data

The technique of computerized tomography

has been used for 3D reconstruction of

shadowgraph projection data. Special apparatus

have been fabricated for performing the

tomography experiments. Convective features as

seen in the shadowgraph images have been

reconstructed over three planes at different

heights above the crystal. Two different

algorithms, namely convolution back projection

(CBP) and algebraic reconstruction technique

(ART) have been employed for the purpose. The

effect of the number of views available for

reconstruction has been studied using projection

data consisting of 18 and 90 views respectively.

Additionally, three different data types namely,

intensity values, contrast (Io-Is)/Is, and refractive

index corresponding to each shadowgraph image

have been used for reconstruction. The influence

of the nature of projection data on the

reconstructed field is studied {Figures 10(a-c)}.

Our results indicate that ART algorithm is able to

reconstruct the broad features in the shadowgraph

images with the 18 view data-set. The fine

features appear when a finer data-set of 90 views

is used. On the other hand CBP is found to

Fig. 6 : Refractive index field corresponding to shadowgraph images at different stages of growth.

Fig. 7 : Deflection of an optical ray as it passes through chamber at two stages of growth. The increased deflections signify the increase of refractive index gradients with growth.

21

Fig. 8 : Infinite fringe Mach-Zehnder interferograms during different forced convection conditions. The solution separates into regions of different concentration in the first case (a & b), while uniform concentration is observed in the second case (c & d) which correspond to Reynolds number of 1600.

(a) (b) (c) (d)

(a) (b) (c)

Fig. 9 : (a-c) Infinite fringe interferograms of the concentration gradient inside the growth chamber at three stages of growth under free convection. (d-f) The computed concentration gradient of the three stages.

Fig. 10 : Tomographic reconstruction contours on a plane above crystal using three types of projection data: (a) Light intensity, (b) Contrast, and (c) Refractive index

(a) (b) (c)

generate several spurious features with the 18

view data-set. These reduce when 90 views are

used. The contour plots of the intensity based

reconstruction bring out the fact that the rising

plumes spread horizontally as they move up into

region of low concentration. The gradients are

seen to be high in the region just above the crystal,

while they are smoother in the bulk of the

crystallizer. This is because under free

convection, the growth process is restricted to a

region adjacent to the crystal. Several cross-

checks have been applied to verify the correctness

22

of the obtained reconstruction. Error estimates

have been computed for the reconstructed

solutions and are found to be small. Tomographic

imaging proves to be a useful diagnostic to obtain

three dimensional character of the convection

(and hence concentration) and its affect on the

growth rate and crystal quality. The shape of the

plume has bearing on the stability of convection

and hence on the quality of the growing crystal.

Interferometric Imaging of Solution

Concentration and Surface Features

A Michelson interferometer has been set up

for measuring minute changes in the solution

concentration due to thermal fluctuations. In

addition it has been used for imaging surface

micromorphology of prismatic and pyramidal

faces of the KDP crystal. Spiral growth

mechanism has been imaged in the form of

concentric fringes of equal thickness for (100)

KDP habit face (Figure 11(a-c)). These originate

from of screw dislocation generated growth

hillocks on the crystal surface. The normal and

tangential growth rates computed from these -5mirco-morphological features are 2.32 × 10

-2mm/min and 2.5 × 10 mm/min. The slope of the

dislocation hillock shown in the above figure is -49.28 × 10 . An interferometric diagnostic that

would enable simultaneous studies of the several

growth influencing parameters has been

developed. The optical schematic of the

composite diagnostic has been shown in Figure 1.

A double Mach-Zehnder interferogram taken

with this diagnostic is shown in Figure 11d. The

circular fringes on the crystal face are due to

screw dislocation, and the wedge fringes provide

flow features. The bend in the fringes near the

crystal edges is due to the solutal boundary layer

in the solid-fluid interface region.

Acknowledgements

The author is grateful to his thesis advisors,

Prof. K. Muralidhar, IIT Kanpur, and Dr. V.K.

Wadhawan, BARC, Mumbai for guidance and

constant motivation. He also expresses his sincere

gratitude to Dr. P.K. Gupta, Head, LMDDD,

RRCAT, Indore and Prof. P. Munshi, IIT Kanpur

for encouragement and support. Thanks are also

due to my colleagues in LMDDD, RRCAT, Indore

for their help and cooperation.

References

1. A.G. Notcovich, I. Braslavsky and S.G.

Lipson, Imaging Fields Around Growing

Crystals, J. Cryst. Growth, 198-199 (1)

(1999) 10-16.

2. L.N. Rashkovich, KDP-Family Single

Crystals; The Adam Hilger Series on Optics

and Optoelectronics (Adam-Hilger, New

York, 1991)

3. I. Sunagawa, K. Tsukamoto, K. Maiwa and

K. Onuma, Prog. Cryst. Growth & Charact.,

30 (1995) 151

4. G.T. Herman, Image Reconstruction from

Project ion: The Fundamentals of

Computerised Tomography, (Academic

Press, New York, 1980)

5. G.S. Settles, Schlieren and Shadowgraph

Techniques, (Springer, Berlin, 2001)

6. K. Muralidhar, Chapter 7, in: Annual Review

of Heat Transfer, 12 (2001) 265-375

Fig. 11 : (a-c) Michelson interferogram (fringes of equal inclination) at successive stages of growth showing the spiral growth mechanism. The position of screw dislocation is marked by ' + '; (d) Double Mach-Zehnder interferogram showing surface as well as solution features.

(a) (b) (c) (d)

23

7. Sunil Verma, K. Muralidhar and V.K.

Wadhawan, Flow Visualization and

Modeling of Convection During the Growth

of K.D.P. Crystals, Ferroelectrics, 323

(2005) 25-37

8. Sunil Verma, Atul Srivastava, Vivek

Prabhakar, K. Muralidhar and V. K.

Wadhawan, Simulation and Experimental

Verification of Solutal Convection in the

Initial Stages of Crystal Growth from an

Aqueous Solution, Ind. J. Pure Appl. Phys.,

43 (2005) 24-33

9. Sunil Verma, K. Muralidhar and V.K.

Wadhawan, Convection and Concentration

Mapping during Crystal Growth from

S o l u t i o n u s i n g M a c h - Z e h n d e r

In ter ferometry and Computer ized rd

Tomography, Proc. 3 Asian Conference on

Crystal Growth & Crystal Technology, Oct.

2005, Beijing, China

10. Sunil Verma, S. Dhawale, V. Bande, K.

Muralidhar and V.K. Wadhawan, Novel

Optical Instrumentation and Apparatus for

Studying Crystal Growth from Solution, rdProc. 3 Asian Conference on Crystal

Growth & Crystal Technology, Oct. 2005,

Beijing, China

11. Sunil Verma, K. Muralidhar and V.K.

Wadhawan, Determination of Concentration

Field Around a Growing Crystal using

Shadowgraphic Tomography, Chapter 14,

in: Computerized Tomography for Scientists

and Engineers, P. Munshi (Ed.), (CRC

Press, New York, USA, and Anamaya

Publishers, New Delhi, 2006) 158-174

12. Sunil Verma and P.J. Shlichta, Optical

Techniques for Mapping of Solution

Properties and Surface Features during the

Growth of Crystals, Prog. Cryst. Growth &

Charact. of Materials (In press, 2007)

13. Sunil Verma, Eglon Depty, K. Muralidhar

and P.K. Gupta, Strength of Free Convection

During KDP Growth and its Relation to

Crystal Quality, (Submitted to Crystal

Growth & Design)

Sunil Verma

Laser Materials Dev. & Devices Division

Raja Ramanna Centre for Advanced Technology

Indore - 452 013.

E-mail: sverma@cat.ernet.in

DO YOU DEAL WITH LASERS AND LASER RELATED PRODUCTS?

DO YOU WANT NEWS ABOUT YOUR PRODUCTS TO HAVE THE WIDEST REACH AMONGST PROFESSIONALS IN THE FIELD?

ILA CAN HELP YOU !!

Dr. L. M. Kukreja

Editor,

R & D Block-B,

Raja Ramanna Centre for Advanced Technology,

Indore-452013 (M.P) India

.

Email: kukreja@cat.ernet.in

Fax: +91-731-248 8380

Tel: +91-731-248 8385

Please Contact

24

Introduction

Terbium aluminum garnet (TAG) is an

interesting opto-magnetic material because of its

low optical absorption and high Verdet constant 1

over a wide spectral region . However, the range

of its applications is limited as the preparation of

single crystals of TAG suitable for practical

applications is still a problem because of its 2

incongruent melting properties . Alternately,

polycrystalline TAG can be used, provided

adequate density and transparency is assured.

Polycrystalline TAG can be prepared either by 3-4

solid state reaction or by sol-gel technique . The

solid state technique results in higher grain size o

because of the high temperatures (>1100 C)

needed to complete the process. Alternately, sol-

gel technique which works at lower temperatures o

(<800 C) is useful for the synthesis of nano-scaled

TAG. Also, this technique is quite suitable for the

preparation of the doped TAG as higher degree of

homogeneity, compared to solid state reaction, 5-6

can be achieved. It has also been observed that

the properties of the material prepared by sol-gel

technique depend on the starting materials as well

as on the type of solvents used. This paper

compares the properties the polycrystalline TAG

powder prepared by sol-gel technique from

oxides (Tb O ) and nitrates (Tb(NO ) .6H O) of 4 7 3 3 2

terbium; aluminum nitrate ( Al(NO ) .9H O) is 3 3 2

used in both the cases.

Experimental

The various steps involved in the sol-gel

preparation of TAG are summarized in Figure 1.

The precursor thus obtained is sintered in air o

at various temperatures in 200-1100 C. The

polycrystalline powder thus prepared is ball

milled for 10-12 hours in acetone medium using

tungsten carbide balls of 20mm diameter. The

powder after ball milling is allowed to dry at room

temperature. The dried powder is characterized

by particle size analyzer (Malvern Instruments

Ltd (UK)-Mastersizer 2000), SEM(FEI USA

Comparison of the Properties of Microcrystalline TAG Powder Prepared by Sol-gel Techniques from Oxides and Nitrates

Fig. 1 : Flow chart showing the steps involved in sol-gel preparation of TAG powder

Articles based on Best Posters presented at NLS-07

25

Model Quanta 200), XRD(Model JSO-Debyeflex

2002 -Rich Seifert & Co, Germany),

FTIR(Bruker Optics USA Model Vertex-70) and

photo-luminescence (PL) (Jobin-yvon Model

flurolog-3) techniques.

Results and discussion

P o w d e r X R D p a t t e r n s a n d t h e

photoluminescence spectra of the TAG powder

prepared from Tb O are identical to that of the 4 7

powder prepared from Tb(NO ) .6H O, indicating 3 3 2

that the crystalline phase is same in both the cases.

The indexed typical powder XRD pattern of TAG opowder sintered at 1100 C is shown in Figure 2(a)

while the photoluminescence spectra excited by

350nm is shown in Figure 2b.

However differences have been observed in

particle size analysis and FTIR spectra of the

respective samples which are discussed in the

following sections.

The observed full width at half maximum

(d ) for the particle distribution (Figure 3) is 0.5

about 3 mm in case of polycrystalline TAG

prepared from nitrate while it is about 10 mm

when oxide is the starting material. This is further

confirmed by SEM micrographs (Figure 4)

where well-dispersed spherical shaped grains of

submicron size are observed in case of TAG

powder prepared from Tb(NO ) .6H O. On the 3 3 2

other hand, in case of the samples prepared from

oxides, relatively more agglomeration and very

few submicron size grains are observed, though a

few particles of almost nano-size are observed,

indicating better suitability of oxide for the

preparation of nano-sized TAG powder.

The FTIR spectra (figure 5) of the precursor -1show strong bands around 3500 cm which is due

to O-H vibrations of the water present in the

precursor. Similarly, the vibrations around 1500

Fig. 2 : Typical powder XRD (a) and Photoluminescence o(b) of the TAG samples sintered at 1100 C.Excitation

wavelength for PL is 350nm.

Fig. 3 : Typical particle size distribution of polycrystalline TAG powder prepared from (a) nitrate and (b) oxide

26

-1cm are due to nitrogen (carbon)-oxy compounds

from nitrates and acetic acid. In case of the oxides -1

there is dramatic decrease in 3500 cm band oabsorption on sintering to 900 C while very little

ochange when the sample is sintered at 1100 C.

Similar type of behavior is observed in case of -1nitrates for the absorption band at 1500 cm . As

seen in Figure 4 the FTIR spectra for the samples o

sintered at 1100 C show very low absorption at -11500 cm implying that the nitrogen(carbon)- oxy

compounds are almost removed on sintering. The -1

absorption at 3500 cm observed in the samples osintered at 1100 C could be due to atmospheric

water adsorbed during the measurements. The -1broad absorption observed in 500-700 cm range

in case of the precursor and samples sintered at o

temperatures below 900 C change into sharp 6 opeaks for the samples sintered at 900 C and

above. This absorption could be due to lattice

vibrations of the TAG; exact assignment is being

worked out.

References

1. C.B. Rubinstein, L.G. Van Uitert, W.H.

Grodkiewicz , J Appl. Phys. 35 (1964) 3069.

2. S. Ganschow, D. Klimm, P.Reiche and

R.Uecker: Cryst. Res. Technol. 34 (1999).

615.

3. Y.pan, M. wu, q. Su, J.Phys. Chem. Solids

65 (2004) 845.

4. W.T.Hsu ,W.H.Wu,C .H .Lu , Ma te r.

Sci.Eng.B 104 (2003) 40.

5. Zhong Y.D.,Zhao X.B.,Cao G.S.,Tu J.P.,Zhu

T.J., J.Alloys Comp.420 (2006),p. 298-305.

6. Nilgun Ozer, Thin Solid Films 304 (1997),

p. 310-314.

Humyra Shabir, Bansi Lal* #

and Mohammad Rafat

Centre for Laser Technology

Indian Institute of Technology Kanpur,

Kanpur - 208 016. #Department of Applied Sciences & Humanities,

Faculty of Engineering & Technology,

Jamia Millia Islamia,

New Delhi - 110 025.

*E-mail : bansi@iitk.ac.in

Fig. 4 : Typical SEM micrograph of polycrystalline TAG prepared from (a) nitrate and (b) oxide

Fig. 5 : FTIR spectra of TAG powders sintered at various temperatures. (a) is the spectra of the TAG sample prepared from nitrate while (b) is that of powder prepared from oxide

27

Introduction

M u l t i s t e p r e s o n a n c e i o n i z a t i o n

spectroscopy (RIS) is a powerful tool to study and

identify the high-lying atomic states. Especially

studies of autoionization states, which are quasi-

bound states of an atom lying above the ionization

threshold of the outer valence electron, has been

of great importance because these states play an

important role to know efficient routes for

resonance ionization in addition to gain 1

fundamental knowledge in atomic physics . The

usual scheme for multistep photoionization

consists of the excitation of an atom from low

lying energy levels to intermediate upper excited

states with a sequence of lasers and subsequent

ionization of excited atom by another laser.

Normally most of this information is acquired by

employing the multistep resonance ionization 2-7

spectroscopy (RIS) in the atomic beam setup .

For refractory elements such as uranium atomic

beam set up is very complex. Brogalia et.al.

recorded three color, three-photon optogalvanic

spectra of uranium in simpler device, hollow

cathode discharge tube (HCDT), where it is used

as a source of atomic vapours source as well as

photoions detector and found reasonable good

agreement with the spectra recorded in atomic 8

beam set up . Levesque et. al. have studied the

single color three-photon ionization spectra of 9uranium in the cathode dark space . Recently

using the same technique Vas Dev et. al. have

studied the single color three photon as well as

two-color three photon photoionization 10

spectroscopy of uranium . The major advantage

of this technique is its ease of implementation. Fig

1 shows homemade HCDT along with routinely

used complex atomic beam setup itself explains

its simplicity and ease of implementation

compared to complicated atomic beam setup.

Researchers further extended it towards

investigations of autoionization states. The even

parity autoionization spectra of calcium are

investigated by S Assimopoulost et. el. using two 11,12color two step excitation . Osamu Kujirai et. el.

studied autoionization states of Lutenium,

Praseodymium and samarium using two color 13-15optogalvanic spectroscopy respectively .

New Autoionization Resonances of Uranium by Three-color Resonance Ionization Spectroscopy in Hollow Cathode Discharge Tube

Fig. 1 : Front view of Home made hollow cathode discharge tube (in circle) which used instead of traditional atomic beam chamber (in rectangle) shows its simplicity

28

We have studied the autoionization states of

uranium by optogalvanic spectroscopy using

three-color three-photon RIS in a U-Ne HCDT in 1the energy region 52850-53180 cm . We have

identified 40 new autoionization states of

uranium and assigned their J values. Some of the

autoionization states were also accessed through

different excitation route.

Experimental setup

Experimental setup used for these studies is

shown in fig 2. It consists of three Nd-Yag -1

pumped dye lasers (spectral width 0.05 cm ,

repetition rate 20 Hz, pulse width 7 nsec), a see

through type home made U-Ne HCDT( cathode

length 30 mm, diameter 8 mm), digital

oscilloscope for signal monitoring and a box car

averager for further signal processing. HCDT was

operated at ~50 mA current. Spatially overlapped

and temporally synchronized three dye lasers

beams (~ 5mm diameter) are made to pas through

the centre of the HCDT and optogalvanic signal

has been detected across a 4 KW ballast resistance.

Results and discussions

Three-color optogalvanic spectrum has been

recorded and analysed using the following

excitation scheme.

In these experiments first & second step

lasers wavelengths (l & l ) were fixed by 1 2

observing the first & second step resonant

optogalvanic signals and photoionization spectra

along with fabry-Perot etalon (FPE) fringes were

recorded by scanning the third laser wavelength

(l ) in the energy region of interest as shown in 3

fig.3a & 3c. To obtain high signal to noise ratio

and avoid single color non-resonant excitation

first and second step dye lasers powers were

attenuated significantly. Three-color three-

photon autoionization spectrum recorded by this

technique consists of resonant single-color (l ), 3

two-color (l +l ), and three-color (l +l +l ) 1 2 1 2 3

optogalvanic features. To extract the three-color

autoionization features from this complicated

spectrum the experiment was repeated with

second laser (l ) blocked. The resultant 2

optogalvanic spectrum consists of single-color

(due to l ) and two-color (due to l +l ) 3 1 3

optogalvanic features only (see fig. 3b). On

comparison of three-color spectrum with the two-

color spectrum, we have identified 40

autoionisation resonances in the energy range 1

52850-53180 cm .

Fig. 2 : Experimental setup

l =566.98 nm1 l =585.85 nm2 l scanned 570-560 nm3

-1 -1 -1620 cm (J=5) 18253.54 cm (J=6) 35319.21 cm (J=6,7)

29

A list of all these resonance with their

proposed J- values is given in table1. Most of the

three-color features are broad as compared to

single and two color features with full width half -1 maximum (FWHM) varying from 0.3 cm -

-14 cm . To the best of our knowledge above

mentioned energy region is not explored by any

researcher so all resonances reported here are new

autoionisation resonances. A part of above

mentioned energy region was also accessed using

following excitation scheme.

Autoionization resonances 29 and 30 as

shown by asterisk in table 1 have also been

observed through above-mentioned route. It has

not only further confirmed our observation of

autoionization resonances seen through first

scheme but also reduced their J value ambiguity

from 5-8 to 5,6.

Conclusion

The autoionization states of uranium have

been studied by optogalvanic spectroscopy using

three-color three-photon RIS, in a simpler device,

a U-Ne HCDT in the energy region 52850-53180 1cm . We have identified 40 new autoionization

states of uranium and assigned their J values.

Part of this energy region has also been studied

using different excitation scheme. The

autoionization resonances identified by both the

schemes reduced J value ambiguity form 5-8 to

5,6.

l =562.81 nm1 l =584.1 nm2 l scanned 570-560 nm3

-1 -1 -1620 cm (J=5) 18342.94 cm (J=4) 35498.38 cm (J=3,4,5)

Fig. 3 : (A) A portion of three- color, three- photon Autoionisation spectrum of uranium observed in HCDT with l =566.98, l = 585.85 and l scanned from 1 2 3

-1561-562 nm in the energy region 53107-53140 cm . (B) Repeat of 1A with second step laser blocked. (C) Fabry-perot etalon fringes

30

Acknowledgement

The authors are thankful to Dr L M

Gantayet, Associate Director,BTDG and Dr A K

Das , Head , L&PTD, BARC, for h i s

encouragement and support. Authors are also

thankful to Mr. G. R. Zende for preparing hollow

cathode discharge tube.

References

1. V S latokov, Laser photoionisation

spectroscopy, Academic press Orlando,

1987

2. B M Suri, K Dasgupta, P N Bajaj, K G

Manohar, R Talukdar, P K Chakraborti, P R

K Rao, J. Opt. Soc. Am. B 4, 1835 (1987)

3. P N Bajaj, K G Mahohar, B M Suri, K

Dasgupta, R Talukdar, P K Chakraborti, P R

K Rao, Appl. Phys. B 47, 55 (1988)

4. K G Manohar, P N Bajaj, B M Suri, R

Talukdar, K dasgupta, P K Chakraborti, P R

K Rao, Appl. Phys. B 48, 525 (1989)

5. V K Mago, B Lal, A K Ray, S D Sharma, P R

K Rao, J. Phys. B: At. Mol. Phys. 20, 6021

(1987)

6. M Miyabe, M Oba, I Wakaida, J. Phys. B :

At. Mol. Opt. Phys. 33, 4857 (2000)

7. B A Bushaw, W Nortershauser, K Blaum, K

Wendt, Spectrochemica Acta Part B 58,

1083 (2003)

8. M Broglia, F Catoni and P Zampetti, J

Physique Coll., 44, C-7, 251 (1983)

9. S Levesque, J M Gagne, F Babin, Can. J.

Phys. 76, 207 (1999)

10. Vas Dev, M L Shah, A K Pulhani, B M Suri,

Appl Phy B 80, 587 (2005)

11. S Assimopoulost, A Bolovinos, A

Jimoyiannis, P Tsekeris, J. Phys. B: At Mol.

Opt. Phys. 27, 2471 (1994)

12. S Assimopoulos, A bolovinos, E Luc-

Koenig, S Cohen, A Lyras, P Tsekeris, M

Aymar, The European Physical Journal D-

Atomic, Molecular, Optical Plasma Physics,

1, 243 (1998)

13. Osamu Kujirai , Youichi Ogawa, Journal of

physical society of Japan, 67, 1056 (1998)

14. Osamu Kujirai , Youichi Ogawa, Journal of

physical society of Japan, 69,2845 (2000)

15. Osamu kujirai, Youchi Ogawa, Journal of

physical society of Japan, 72, 1057 (2003)

M. L. Shah, Vas Dev and B. M. Suri

Laser and Plasma Technology Division

Bhabha Atomic Research Centre,

Mumbai - 400 085.

E-mail : mlshah@barc.gov.in

31

Abstract

We report results of a study carried out to

investigate the effect of He-Ne laser (632.8 nm)

irradiation on hair follicle cycle in control and

testosterone treated male albino mice. Optical

Coherence Tomography (OCT) and histology

were used to measure the mean hair follicle length

and the number of hair follicles in different

phases. While the anagen to catagen length ratio

measured by both the techniques was nearly the

same, the length of the hair follicles measured by

the two techniques differed by a factor of 1.5 with

histology showing smaller length. In both control

and the testosterone treated mice, He-Ne laser 2irradiation at 1 J/cm led to a significant increase

(P<0.05) in % anagen indicating stimulation of

hair growth.

Introduction

Androgenetic alopecia (AGA) is the most

common form of hair loss. This is believed to be

associated with changes in hair follicle cycle from

active anagen stage to inactive catagen stage and

stepwise miniaturization of the hair follicles,

induced by the action of dihydrotestosterone, an

enzymatic product of testosterone. Although

modulators of androgen metabolism or hair

growth promoters are used for the treatment of

AGA, these often induce several adverse side

effects and their clinical responses are poorly 1understood . More recently, several pre-clinical

2-4and clinical studies have reported that exposure

to low level laser therapy has positive influence

on hair growth parameters like the number of hair

follicles and the tensile strength of the hair.

However, no detailed scientific study exists that

validates these data.

Previous studies in mice and hamsters have

demonstrated that exogenously administered

testosterone inhibits telogen to anagen 5,6

transformation . Therefore, we have investigated

the effect of He-Ne laser (632.8 nm) irradiation on

mice skin (i) subjected to exogenously

administered testosterone treatment and (ii)

without treatment and, using optical coherence

tomography (OCT) and histology. Changes in the

hair follicle length and the number of hair follicles

in active growth stage ‘anagen’ and in regressing

stage ‘catagen’ were assessed using both OCT and

histology.

Materials and Methods

Animals: Swiss albino mice with body mass

~30 gm aged ~3 months were used for the study.

During the experimental period all animals were

kept in individual cages and reared in controlled 0environment (27 ± 1 C, 12 hour light and dark

cycle), fed commercial diet and allowed free

access to tap water. In each animal an area of ~ 2 2

cm on the dorsal side of abdomen was shaved.

The animals were divided into 6 groups of 3

animals each; G-I: control group that was neither

given testosterone treatment nor He-Ne laser

irradiation, G-II and III: mice in which the pre-

shaved skin region was irradiated with He-Ne

laser (at 24 hour interval for 5 days), at a dose of 1 2 2

J/cm and 5J/cm respectively, G-IV, testosterone

treated mice, G-V and VI: testosterone treated

mice in which the pre-shaved skin region was

irradiated with He-Ne laser (at 24 hour interval

for 5 days, on the same day of testosterone 2 2treatment) at a dose of 1 J/cm and 5 J/cm

respectively.

Testosterone treatment: 100µlof 10 mg/ml

Testosterone suspension (Aquaviron, Nicholas

Piramal India ltd.) was injected subcutaneously

into the animals at 24 h interval for 5 days.

He-Ne Laser irradiation: Prior to

irradiation, the animals were anesthetized by an

intra peritoneal injection of Ketamine

Hydrochloride (80 mg / kg). The shaved animal

skin region was exposed to a He-Ne laser beam

(l=632.8 nm, power out put ~ 10.5 mW)

expanded to a circular spot of the diameter 1.6 cm,

Effect of He-Ne Laser Irradiation on Hair Follicle Growth in Testosterone Treated Mice Investigated

with Optical Coherence Tomography and Histology

32

which results in a power density of ~ 5.25 2

mW/cm at the sample plane. The exposure time

was varied from ~ 190 seconds to ~ 950 seconds to 2achieve the irradiation doses of 1 J/cm and 5

2J/cm , respectively.

Use of OCT for the analysis of mice skin: On ththe 7 day of the experiment the animals were

sacrificed and the total shaved skin region from

each group was excised and used for imaging by

optical coherence tomography (OCT). The OCT

system which had an axial resolution of ~12 mm

used a 840 nm super luminescent diode (SLD)

with bandwidth of 40 nm as light source. With the

10 X objective used for focusing the beam on the

sample the lateral resolution of the system was

~20mm (Fig. 1). The measured signal to noise

ratio of the system was ~100 dB. The time taken

for acquiring an image was about a minute. The

acquired back-scattered intensity distribution of

the cross-section of the sample is displayed as a

gray scale image. The details about the 7experimental setup can be found in reference .

From the cross-sectional images measurements

on the hair follicle length and the number of hair

follicles in different stages of growth were carried

out.

Histopathological analysis of skin: After

OCT image acquisition, the tissue sample from all

the groups was processed using standard

histological treatment, i.e., 10 % formalin

fixation, alcohol processing and paraffin 8

embedding . The paraffin embedded samples

were cut longitudinally into sections of 4 µm

thickness with a YSI-118 microtome

®(YORCO CRYOSTAT, India) and stained with

haematoxylin-eosin. The tissue sections were

examined by bright field microscopy (Axiovert

135, Zeiss, Geramny) at 40 X magnification and

measurements on the hair follicle length and the

number of hair follicles in different stages of

growth were carried out. The anagen (growing

stage) and catagen (regression stage) hair follicles

were identified on the basis of their histological

features. While anagen follicles have fully grown

hair bulb and their root located near the

panniculus carnosus, catagen follicles possess

regressed hair bulbs, span the upper part of dermis

and thus their total length is reduced considerably.

Results and discussion

In Figure 2 (a-f) we show the histological

images of the skin samples of group G-I-VI,

respectively. From the microscopic images, the

measured length of the anagen and catagen

follicles in control and testosterone treated

samples were 346 ± 30 mm and 132 ± 10.8 mm

respectively. There was no significant difference

in the measured length of the hair follicle for

experimental groups. In Figure 3 (a-f) the OCT

images of the resected skin samples of all the

groups (G-I-VI) are shown. From these images,

the mean length of the anagen and catagen

follicles in control and testosterone treated

samples were measured to be 475 ± 40mm, 200 ±

20 mm respectively. It may be noted that, while the

Fig. 1 : Schematic of OCT setup. SLD-super luminescent diode; PD-photodiode; TIA-transimpedence

amplifier; DAQ-data acquisition board.

Figure 2: Histological images of (a) control sample; G-

I, (b) control sample subjected to He-Ne laser dose of 2 1J/cm ; G-II, (c) control sample subjected to He-Ne

2laser dose of 5 J/cm ; G-III, (d) testosterone treated

sample; GIV, (e) testosterone treated sample subjected 2to He-Ne laser dose of 1J/cm ; G-V,(f) testosterone

2treated sample subjected to He-Ne laser dose of 5 J/cm ;

G-VI. ( ): anagen. ( ): catagen. Scale bar: 100mm.

33

anagen to catagen length ratio measured by both

the techniques is nearly the same (~2.5), the

measured length of follicles by OCT imaging was

~ 1.5 times longer than that by histology. This is in 10,11qualitative agreement with previous reports

which suggest that processing of skin sample for

histopathology leads to shrinkage of the tissue,

which may vary from a factor of 1.5

to 2.5.

In figure 4 we show the pie chart data of the

relative percentage of anagen, catagen and

telogen hair follicles in skin of mice for group G1

to G V1. In the control skin (G-I, 4 a), a majority

(~ 60 %) of the hair follicles were in anagen stage. 2Exposure to He-Ne laser at a dose of 1 J/cm (G-II,

4 b) led to significant increase in % anagen

compared to that of the G-I. This indicates

stimulation of hair growth by low level of He-Ne

laser irradiation. Exposure to He-Ne laser 2

irradiation at a dose of 5 J/cm (G-III, 4 c),

however, led to a significant decrease in % anagen

with respect to that of the G-I, indicating

suppression of hair growth at this dose.

Testosterone treatment (G-IV, 4 d) led to the

inhibition of hair growth, which was

characterized by a significant increase in %

catagen follicles with respect to that of G-I. In the

testosterone treated skin, exposure to He-Ne laser 2

at a dose of 1 J/cm (G-V, 4 e) caused a significant

increase in % anagen, indicating enhancement of

hair growth whereas, exposure to He-Ne laser at a 2

dose of 5 J/cm (G-VI, 4 f ), showed no significant

changes.

The results presented in Figs 2, 3 and 4

indicate that a low dose of He-Ne laser may

promote growth of hair in mice. The results are in

agreement with earlier reports which demonstrate

that exposure to low level laser radiation leads to

augmentation in proliferative and synthesizing 12,13

activity of cells . It must also be noted that in our

study, the hair growth promotion with respect to

the respective control was much larger for the

testosterone treated mice suggesting a better

response of cells growing at slower rate or under

stress conditions to stimulatory effects of low

dose laser irradiation. This is in conformity with 14,15

studies reported previously . In contrast to the 2irradiation dose of 1 J/cm , a suppression of hair

growth was observed in the samples irradiated at 5 2

J/cm . This result is in accordance with several

other previous studies, which suggest that while at

lower dose, the low level of ROS generated leads 16

to stimulatory effect ,at higher dose and the

resulting high level of ROS, inhibitory effects are 17,18seen .

Conclusion

Fig. 3 : OCT images of (a) control sample; G-I, (b) 2control sample subjected to He-Ne laser dose of 1J/cm ;

G-II, (c) control sample subjected to He-Ne laser dose of 25J/cm G-III, (d) testosterone treated sample; GIV, (e)

testosterone treated sample subjected to He-Ne laser 2dose of 1J/cm ; G-V,(f) testosterone treated sample

2subjected to He-Ne laser dose of 5J/cm ; G-VI. Solid arrow: anagen. Dashed arrow: catagen: image size: 1.5 mm (depth) x 3 mm (lateral).

Fig. 4 : Relative percentage of anagen, catagen and telogen hair follicles in skin of mice for group G1 to G V1. (a) control sample; G-I, (b) control sample subjected

2to He-Ne laser dose of 1J/cm ; G-II, (c) control sample 2subjected to He-Ne laser dose of 5J/cm G-III, (d)

testosterone treated sample; GIV, (e) testosterone 2treated sample subjected to He-Ne laser dose of 1J/cm ;

G-V,(f) testosterone treated sample subjected to He-Ne 2laser dose of 5J/cm ; G-VI.

34

The results of our study show that He-Ne 2

laser irradiation at 1 J/cm leads to a promotion of

hair growth in mice skin and the effect was more

pronounced in testosterone treated mice. An 2

increase in the dose to 5 J/cm led to regression of

hair growth. Use of OCT imaging for

visualization of changes in the size of hair

follicles has also been demonstrated. This may be

helpful in monitoring skin pathologies associated

with alopecia.

References

1. R M Trueb. Exp Geront, 7,981-990 (2002).

2. E Mester, B Szende, ,P. Gartner, Radiobiol.

Radiother, 9, 621-26 (1968).

3. J L Satino, M. Markou, Int J Cos Surg. and

Aest Dermatol, 5, 113 –117 (2003).

4. S S Kim, M W Park, C J Lee, J Am Acad,

Dermatol P1502: AB112 (2007).

5. Mezick JA, Gendimenico GJ, Liebel FT,

Stenn KS. Br J Dermatol 1999; 140: 1100-4.

6. Sundberg JP, King LE, Bascom C. Eur J

Dermatol 11, 321-5, 2001.

7. K.D. Rao, Y. Verma, H.S. Patel, and P.K.

Gupta, Curr. Sci., 90, 1506 -10 (2006).

8. Agnihotri S, Sachdeo S, Sharma A, Keerti V,

Gupta P K. Laser Life Sci 1996; 7(4): 227-

235.

9. Ma L, Chan K, Nigel J, Smith T, Wu A, Tian

L, Lam A. Euro J. Immunology 2005

;35:3365-74

10. S. Hendrix, B. Handjisk, E.M.J. Peters, R.

Paus, J Invest Dermatol, 125:42-51, (2005).

11. R. Kuranov, V. Sapozhnikova,D. Prough,I.

Cicenaite and R. Esenaliev, Appl Opt, 46,

1782-86, 2007.

12. Yu H S, Wu C S, Yu C L, Kao Y H, Chiou M

H. J Invest. Dermatol 2003; 120: 56-64.

13. Kipshidze N, Nikolaychik V, Keelan M H, et

al. Lasers Surg. Med 2001; 28: 355-64.

14. Karu T, Pyatibrat L V, and Kalendo G S.

Nuovo Cimento D 9 1987b; 1485-1494.

15. Mognato M, Squizzato F, Facchin F,

Zaghetto L, Corti L. Photomed Laser Surg

2004; 22(6): 523-6.

16. Grossman N, Schneid N, Reuveni H, Halevy

S, Lubart R. Lasers Surg. Med 1998; 22 (4):

212-8.

17. Pal G, Dutta A, Mitra K, Grace M S. et al. J

Photochem Photobiol B 86: 252-261.

18. Young G K, Sok C P, Sang R L. Laser Surg.

Med 2000: 27: 420-426.

Sunita Shukla*, Yogesh Verma,

Khageswar Sahu, K Divakar Rao,

Alok Dube, and Pradeep Kumar Gupta

Laser Biomedical Applications &

Instrumentation Division, Raja Ramanna Centre for Advanced Technology,

Indore - 452 013.

35

where m is order, d is groove density, q incidence i

angle q diffraction angle, l is wavelengthd

Cavity wavelength Nl/2 = AB + BC (cavity length) where N is the longitudinal mode index number

AB = L Sin q & BC = L Sin qi d

Nl/2 = L (Sin q + Sin q ) (2)i d

From Equation (1) & (2)

N = 2mL/d (3)

Equation (3) indicates that the longitudinal index number (N) does not depends on the

diffraction angle q and lasing wavelength l and d

hence does not change, while rotating the tuning mirror. This implies that there will not be any mode hop, while tuning the laser if we match the cavity pivot point carefully.

The end mirror was fixed with epoxy adhesive to a piezoelectric transducer (PZT) stack, which provides a maximum displacement

of 10mm at a drive voltage of 1 kV. The tuning mirror is fixed on a two-stage rotational table with coarse and fine tuning mechanisms. The first stage provides coarse movement with a minimum resolution of 25.92 arc-sec with a stepper motor of 50,000 micro-steps per revolution. The second stage is used for fine motion. It gives a minimum

resolution of 0.0014 arc-sec. A 20mm PZT with drive voltage of 1 kV was used in series with motorized mike at the tuning arm of length 100 mm.

A part of the SLM laser beam was used for beam diagnostics such as linewidth, wavelength and ASE measurement. The schematic of the laser is shown in fig2.

Single Longitudinal Mode Selection

The SLM cavity is a short one so that the longitudinal mode spacing exceeds the single pass bandwidth of the laser. The cavity length of 50 mm gives a cavity mode spacing of 3 GHz.

Performance Characteristics of Remotely Tunable, High Repetition Rate, Copper Vapor Laser Pumped Single Longitudinal Mode Dye Laser

Introduction

Pulsed tunable, high repetition rate (>6kHz) single longitudinal mode dye lasers are of interest to atomic laser isotope separation, trace analysis and precision nonlinear laser spectroscopy. For certain applications, mode hop free scanning over a wide wavelength range is required. Various resonator configurations have been reported in literature to obtain single longitudinal mode

1-3pulsed dye laser . In this paper, we report the performance characteristics of a remotely tunable grazing incidence grating, single longitudinal mode pulsed dye laser, pumped by 6 KHz Copper Vapor Laser (CVL), developed in our lab. Mode hop free scanning over 70GHz is reported.

Single Longitudinal Mode Dye laser

The SLM GIG dye laser developed in our lab is a short cavity laser (length ~5 cm) based on the

4,5design of of Littman . The cavity comprises an indigenously designed flow through dye cell (5mm x 1mm cross section), high reflectivity (R > 99%) end mirror, GIG grating (2400 lines/mm groove density) and a tuning mirror (R>99%). The output of the dye laser was obtained from the zeroth order of the grating.

The axis of rotation of the tuning mirror passes through a geometrically located point known as pivot point. The surface planes of the tuning mirror, end mirror and grating intersect on this pivot point (fig. 1).

The emission wavelength of the laser is determined by the relation,

ml = d (Sin q + Sin q ) (1)i d

Fig. 1 : Schematic of Cavity Configuration

36

0Grating is kept at an angle of incidence of 89 to provide high dispersion for the laser.

The single pass line width of the grating mirror pair is given by (4)

(4)

The single pass line width is calculated to be 1.5 GHz for grating length l=62.5 mm. Since the single pass line width is half of the mode spacing, single longitudinal mode is selected by the cavity. For SLM mode operation, single transverse mode is achieved by the focal spot of pump beam as it act as an aperture for filtering higher order modes. The size of the focal spot should be optimum for SLM operation. Too small a spot size increases the diffraction losses and a larger spot size leads to multimode operation.

Experimental results

The SLM dye laser was longitudinally pumped with green component of the CVL beam. The green component (510.6 nm) of copper vapor laser operating at 6 kHz repetition rate was focused into the gain medium with plano convex lens of focal length 200 mm. The size of the focal spot in the gain medium is ~ 160 micrometer. The flow velocity of ethanol (2.55 m/sec) is sufficient to clear the flow with flow clearance ratio 2.5. the regions of concern are those with higher shear near the liquid solid interface where the average velocity varies from zero at the wall to the free stream velocity at some distance. We have carried out detailed computational fluid dynamicssimu-lation to design and fabricate flow through cells for the SLM dye laser resulting in higher flow velocities with out vortices and low pressure drop.

The linewidth of the laser spectrum was measured with Fabry Perot etalon of FSR 7.5 GHz

and CCD camera. The Fabry Perot spectrum of SLM dye laser is shown in fig 3. The line width was reduced from 850 MHz to 510 MHz by increasing the incidence angle of grating from

0 088.5 to 89.05 . The SLM dye laser wavelength was tuned using central stepper motor and PZT attached to tuning mirror through a 100 mm mechanical arm. Tuning range of SLM laser was varied between 556.4 nm to 568.5 nm using commercial wavelength meter. The smaller tuning range of 12 nm for SLM dye laser results

0from the GIG configuration with 89 angle of incidence, which leads to high loss in the cavity. At this grating angle, the diffraction efficiency in the first order is around 1%, which is close to the efficiency of laser. Using a grating with higher diffraction efficiency will lead to higher energy conversion efficiency of SLM dye laser.

The amplified spontaneous emission (ASE) was measured with monochromator grating and photodiode. The ASE was reduced from 0.5% to 0.027% by increasing angle between pump beam and dye laser beam to 4.7 degree. Since the laser beam is obtained from the zeroth order of grating, the angle between the dye laser axis and pump beam axis is a critical parameter for minimization of ASE.

The FWHM of the SLM dye laser pulse was measured to be 20 ns for a pump pulse duration of 30 nsec. The dye laser beam divergence was measured to be 0.648 mrad. SLM laser output of 16mW was obtained with an efficiency of 1.6%. The CVL beam size was telescopically reduced from 40mm to 10mm. The CVL beam was spatially filtered using a pinhole of diameter 700µm. The SLM dye laser efficiency was improved from 1.6% to 2.3% with an increased output power of 95mW at 3.8W CVL green beam. Beyond this pump power, a second mode started

Fig. 2 : The schematic of the laser

Fig. 3 : The Fabry Perot spectrum of SLM dye laser

37

appearing on and off as expected from spatial hole burning effect.

The experimental results are tabulated in Table1

Mode Hop Free Wavlength scanning of SLM dye laser

SLM dye laser was remotely tuned with the

20 mm PZT fixed on the tuning mirror by applying a slowly varying voltage (ramp) from 0 – 1kV. The input signal was generated from the computer and fed to the high voltage amplifier of the PZT. The high voltage signal was fed to the PZT at the tuning mirror. Using this technique mode hop free tuning over a wavelength range from 559.75556 nm to 559.74642 nm (~ 70 GHz) was achieved. Laser wavelength meter and FP etalon fringes monitored the mode hop free tuning of the SLM dye laser. The cavity mode spacing is 3 GHz (~ 3 pm) for 5 cm cavity length. While tuning the SLM laser the sudden jump of 3 GHz (Cavity FSR) in the wavelength was not detected in the wavelength meter, indicating mode hop free tuning.

Single pulse Spectrum

The bandwidth of SLM dye laser was measured with FP etalon of 7.5 GHz and wavelength meter (WS-7L). A fast CCD camera was externally triggered to measure the single shot single pulse bandwidth of the SLM dye laser. Thirty-five frames of single shot single mode FP fringes are shown in the fig 2. The time average bandwidth was measured as ~375 MHz and the single pulse bandwidth was 315 MHz as shown in fig 3.

Conclusion

A compact, short cavity, remotely tunable, high repetition rate grazing incidence grating single longitudinal mode dye laser with mode hop free scanning over 70 GHz has been developed.

The average and single linewidths achieved were 375 MHz and 315 MHz.

Reference

1. Littman M .G.1984, Appl.Optics, 23, 4465 .

2. Hansch T., 1972, Appl.Optics, 11, 895 .

3. Bernhardt A.F. and Rasmussen P., 1981, Appl.Phys.B, 26, 141 .

4. Littman M.G. and Metcalf H.J, 1978, Appl. Optics, 17, 2224 .

5. Liu K. & Littman M.G., Opt. Lett. 6, 117 (1981).

*Sunita Singh, G Sridhar, VS Rawat, N. Kawde, AS Rawat, SK Mishra, LM Gantayet

Laser & Plasma Technology DivisionBhabha Atomic Research Centre,

Mumbai - 400 085*E-mail : sunit@barc.gov.in

Table 1

Minimum average linewidth

of the SLM laser 375 MHz

Energy conversion Efficiency 2.3%

ASE 0.027%

Pulse duration (fwhm) 20 nsec

Tuning range 12nm

Fig. 4 : Single shot fringes from fast CCD Camera

Fig. 5 : Intensity pattern of interferogram for single pulse

38

In the recent times, there has been a

considerable interest in enhancing the absorption

of high intensity ultrashort laser pulses during 1-3their interaction with matter . The enhanced

absorption is manifested in the observation of

energetic electrons, MeV ions and x-rays. The x-

rays are useful as a micron sized source which has

many potential applications e.g. time resolved

XRD studies, x-ray lithography etc. Since the

absorption of high intensity ultrashort laser pulses

by planar solid targets is considerably low (~10-

20%), various types of targets like gratings,

structured targets, pre-deposited metal clusters,

gas clusters, snow clusters etc. have been used to 4

enhance coupling of laser energy in matter . The

increased deposition of fs pulse energy in grating

targets and pre-deposited metal clusters has been

achieved through plasmon resonance and field

enhancement in protrusions. However, since

gratings are expensive, they are practically

unusable on routine basis as targets for x-ray

source.

High absorption (80-90%) of ultrashort

laser pulses has also been observed in gas atom 5clusters . The interest in clusters stems from the

fact that the electric field inside the cluster is

highly enhanced at three times the critical density 5-8

(n ) due to resonance. As the clusters absorb the c

laser energy, they get heated up and start

expanding. During expansion, the density

decreases (from near solid density). When the

density approaches 3n , the absorption increases c

rapidly due to enhancement of the electric field 7,8inside the cluster . However, the keV x-ray

conversion from such clusters is rather small

(~0.01%) and it is also of long duration of few tens

of ns. This limits the use of gas atom clusters as an 5,7,8x-ray source . Further, metal clusters have also

been used as targets for efficient laser energy

absorption. They can be produced by high

pressure dc sputtering on polished disks, or by

magnetron gas aggregation. They can also be

produced by atom pick-up method. All these

methods involve two steps, first depositing the

clusters on a planar solid substrate, and then using 9them as target for plasma formation .

Recently, intense femtosecond laser

irradiation of solid targets has been proposed as a

simple means of synthesis of clusters with

diameter ~10-50 nm. The reason of formation of

clusters is the relaxation of material in extreme

conditions via fragmentation and molten material 10

ejection . We have shown in our earlier

experiments efficient large cluster formation (size

10-80nm) using 300 ps laser pulses focussed on 11-12

various targets like Ag, In, Cu etc which may

be used as targets for x-ray generation. In this

paper, we present a study of the energy absorption

of intense Ti: Sapphire laser pulses in such in situ

produced clusters, and the x-ray generation from

them. A high absorption (exceeding 70%) of the

45 fs laser pulses is observed at an intensity of 17 23x10 W/cm . Further, a high x-ray conversion

efficiency (hn ³ 1 keV) of ~ 0.1% is observed

which is much higher than that achieved from gas

clusters or planar solid targets. This suggests that

the in situ produced solid clusters are better

targets for x-ray generation than the gas clusters

and solids. In addition, the present method offers

a simple single-step alternative for keV x ray

generation compared to the structured targets or

pre-deposited clusters.

Figure 1 shows a schematic of the

experimental setup. The stretched 300ps laser

pulse before the grating compressor was split by a

pellicle beam splitter and it was used to produce

metal clusters by focussing it on a planar solid

A Novel Technique of Intense keV X-ray Generation from in situ Laser Produced Silver Clusters

Fig. 1 : Schematic of the experimental setup

39

target of silver in normal incidence geometry.

This pulse is referred to as the cluster forming

“prepulse beam”. The focussed intensity of the 10 12prepulse beam was varied between 10 – 4x10

2W/cm . To study the clusters generated by solid

target irradiation at different intensities, the

plasma debris deposition was taken on a substrate

kept at a distance of 5 cm from the target. Fig.2

shows the SEM pictures of the deposit taken at

two prepulse intensities, one at a high intensity of 12 2 103x10 W/cm and the other at low intensity 10

2W/cm . Fig 2.a clearly shows a much higher

cluster density corresponding to the deposition

taken at the higher intensity of the prepulse. The 12 2

particle density in this case (3x10 W/cm ) was

estimated from the SEM pictures to be ~ 100 2 11,12

particles/mm .

The absorption of intense femtosecond laser

pulses was measured using the experimental

setup shown in Fig.1. The transmitted part of the

uncompressed beam through the pellicle beam

splitter was time delayed through a delay setup

and then compressed for getting a pulse of 45 fs

duration (referred to as the fs “main beam /

pulse”). This main beam (70 mJ, 45 fs) was

focussed very close to the target, at a distance of

~30 mm from the target surface. This beam

propagated parallel to the target surface and

irradiated the clusters emanating from the

prepulse beam irradiating the target. For

absorption measurements, the main beam energy

was measured with / without prepulse produced

plasma in its path, to get normalized transmission

through the plasma plume. In order to take care of

any divergence of the main laser beam

propagating through the plasma, the transmitted

light was collected using a large diameter lens (75

mm diameter, 100 mm focal length ) and made

incident on a pyro-electric detector (Gentec,

sensitivity 3V/J). Another more sensitive

calorimeter (Gentec, sensitivity 164 V/J) was

placed outside the chamber to sample the

scattered light collected by another lens of focal

length 50 mm placed on the plasma chamber wall 0 window, in a direction of 45 w.r.to the target. The

scattering signal was very low, almost at the noise

level. The angle integrated scattered laser light

intensity normalized to the incident beam was

£1%. Thus the reduction in transmission of the

main pulse beam is predominantly due to its

absorption by clusters. Next, an x-ray p-i-n diode

(Quantad, USA) filtered with two alumnized

polycarbonate filters having a cut-off (1/e

transmission) at 1 keV) was used to measure the

x-ray radiation emitted from the laser irradiated

clusters. The detector subtended a solid angle of

410 m sr at the source

The absorption measurement of the

femtosecond pulses in the in situ produced silver

clusters was carried out for two delays of 10 ns

and 75 ns. In the case of 10 ns delay, a low

absorption was observed . The absorption was

<10% even at the maximum prepulse intensity of 12 24x10 W/cm . This may be due to the non-arrival

of the clusters in the interaction zone with the

main laser beam which propagated at a distance of

~30 mm from the target surface. Hence the delay

between the prepulse and the fs main pulse was

increased to 75 ns. The absorption measurements

were carried out at the maximum intensity of the 17 2

main laser beam of 3x10 W/cm for different

intensities of the prepulse beam.

Figure 3 shows the variation of the main

pulse absorption with the prepulse beam intensity 17 2

at the main pulse intensity of 3x10 W/cm . It is

seen from this figure that the absorption increases

with prepulse intensity, reaching a maximum

Fig. 2 : SEM pictures of deposition of Ag nanoparticles 12 2at two intensities of the prepulse ( a) at 3x10 W/cm ( b)

10 2at 10 W/cm

40

value of ~70% at the maximum prepulse intensity 12 2

of 4x10 W/cm . The observed increase in

absorption with prepulse intensity is simply

understood from the increase in number of

clusters produced at higher prepulse intensity. As

noted earlier from the SEM pictures (Fig.2), a

higher cluster density was observed for a higher

prepulse intensity.

It may be relevant to mention that a high

absorption was observed only when a fresh

surface of the target was irradiated. When the

prepulse laser beam was incident on a previously

irradiated spot on the target, the absorption

decreased. Fig.4 shows the variation of the main

pulse absorption with the number of prepulse

shots fired at the same place. It is seen that the

absorption decreases with the number of prepulse

shots, but it does not reduce to zero. This behavior

may be understood as follows. When the prepulse

irradiates a solid surface, it forms a crater. On

subsequent laser irradiation at the same spot, there

will be a recession of the crater surface as more

and more material comes out. Thus the

nanoparticles produced from irradiation of crater

region will take a longer time to reach the fs laser

beam and would increasingly miss interaction

with the fs beam. Next, as stated above, the

absorption did not reduce to zero even after a

number of shots were fired at the same place. This

may be due to arrival of some lighter

nanoparticles in the interaction region even after

crater formation.

Next, we present the results of the x ray

emission measurements from the heating of in situ

produced clusters. Fig.5 shows the intensity of x-

ray emission as a function of the prepulse beam

intensity at a maximum main laser pulse intensity 17 2

of 3x10 W/cm . It is seen that the x-ray intensity

increases with prepulse beam intensity. This

behaviour is consistent with our measurements of

a higher absorption of fs pulse at high prepulse

intensity. With an increasing number of clusters

interacting with the main pulse, the absorption

increases and it also enhances the plasma

temperature. Since the radiated power has a

strong dependence on temperature, x ray yield

also increases with increasing absorption. The

spectrally and temporally integrated x-ray yield

(hn ³ 1 keV) at the main laser pulse intensity of

Fig. 3 : The variation of the main laser pulse absorption as a function of the prepulse laser intensity at main

17 2pulse intensity of 3x10 W/cm .

th Fig. 4 : Variation of the absorption of fs pulse with n pre pulse shot fired at the same place in silver targets. The fitted curve is only guide to the eyes

Fig. 5 : X-rays emission intensity from silver clusters as a function of the prepulse intensity at main laser

17 2intensity of 3x10 W/cm .

41

17 23x10 W/cm and at the prepulse intensity of

12 2 4x10 W/cm was measured to be ~ 60 mJ. This

gives a percentage conversion efficiency of the -2 laser energy into x-rays of ~ 8.5x10 %. This x-ray

conversion is much higher than that observed

from ultrashort pulse intense irradiation of rare

gas clusters or planar solid targets. Next, the

FWHM duration of the p-i-n diode signals was ~ 8

ns (detector limited). This stands in contrast with

the x-ray emission from gas cluster plasma where

much longer x-ray emission (40 - 150 ns) has

been reported. The long pulse duration signifies

emission coming from the expanding cluster 5

plasma, during the hydrodynamic expansion .

In conclusion we have shown a high

absorption of ~ 70% of high intensity ultrashort

laser pulses in metal clusters in situ produced by a

sub-ns prepulse. Effect of temporal delay

(between the prepulse and the main pulse), and

prepulse intensity was studied to achieve high

absorption of the fs pulses in these clusters. The

high laser light absorption resulted in an efficient

keV x-ray generation. A high conversion -2

efficiency of ~8.5x10 % of laser energy into x-

rays (hn ³ 1 keV) is observed. Moreover, the x-ray

emission in directions making large angle with

target normal is nearly debris free. This is because

while x ray emission from the in-situ produced

clusters is expected to be isotropic, the debris

expands predominantly in a direction normal to

the target. The present scheme of cluster

formation has also the advantage that the

generated clusters are slightly away from the solid

target. This prevents heat conduction from

clusters to the cold substrate beneath leading to

enhanced plasma temperature and increased x-

ray emission.

Acknowledgements

The authors will like to thank B.S.Rao,

V.Arora , J .A.Chakera , H.Singhal and

S.R.Kumbhare (all from LPD, RRCAT) for their

support during the experiment. The authors would

also like to thank H. Srivastava and M.K.Tiwari of

ISUD, RRCAT for their help in SEM images.

References

1. A.McPherson, B.D.Thomson, A.B. Borisov, K.Boyer, and C.K.Rhodes, Nature 370, 6491 (1994).

2. M.M.Murnane, H.C.Kapteyn, S.P.Gordon, J.Bokor, E.N.Glytsis, R.W.Falcone, Appl.Phys. Lett. 62, 1068 (1993)

3. S.P. Gordon, T Donnelly, A.Sullivan, H. Hamster, and R.W Falcone. Optics Letters 19, 484 (1994)

4. G.Kulcsar, D.A.Mawlawi, F.W.Bundnik, P.R.Herman, M.Moskovits, L.Zhao, and R.S Majoribanks, Phys. Rev. Lett. 84, 5149 (2000)

5. T.Ditmire, R.A.Smith, R.S.Marjoribanks, G.Kulcsar, M.H.R.Hutchinson, Appl. Phys. Lett. 71,166 (1997).

6. H.Singhal, V.Arora, P.A Naik, and P.D Gupta, Phys. Rev. A 72, 043201 (2005)

7. S.Sailaja, R.A.Khan, P.A.Naik, and P.D.Gupta, IEEE Trans. Plasma Sci. 33, 1006 (2005).

8. T.Ditmire, T.Donnelly, R.W.Falcone, M.D.Perry, Phys. Rev. Lett. 75, 3122 (1995)

9. P.P.Rajeev, P.Taneja, P.Ayyub, A.S.Sandhu, G.R.Kumar, Phys. Review Lett. 90, 115002 (2003)

10. S.Amoruso, R.Bruzzese, N.Spinelli, R.Velotta, M.Vitiello, X. Wang, G.Ausanio, V.Lannotti, and L. Lanotte, Appl. Phys. Lett . 84, 4502 (2004).

11. R.A.Ganeev , U.Chakravarty, P.A.Naik, H.Srivastava, C.Mukherjee, M.K.Tiwari, R.V.Nandedkar, and P.D.Gupta, Appl. Optics 46, 1205 (2007)

12. R . A . G a n e e v, A . I . Ry a s n y a n s k i y, U.Chakravarty, P.A.Naik, H.Srivastava, M.K.Tiwari, and P.D. Gupta, Appl. Phys. B 86, 337 (2007)

U.Chakravarty, P.A.Naik,

R.A.Khan, and P.D.Gupta

Laser Plasma Division, Raja Ramanna Centre for Advanced Technology,

Indore - 452 013.

E.mail : uday@cat.ernet.in

42

Best Thesis awards

In the PhD thesis presentation session organized during the seventh DAE BRNS National Laser Symposium (NLS-07), there were 7 theses presentations. The judges selected following four theses at par for the award:

1. Bose-Einstein Condensation in a Quasi-Electrostatic Trap

Saptarishi Chudhuri, Tata Institute of Fundamental Research, Mumbai

2. A Study of Diode Pumped Solid State Lasers.

Jogy Goerge, Solid State Laser Division, Raja Ramanna Centre For Advanced Technology, Indore.

3. Development and Application of Optical Diagnostics for Imaging Crystal Growth from Solution

Sunil Verma, Laser Materials Development and Devices Division, Raja Ramanna Centre for Advanced Technology, Indore.

4. Study of Ultra Cold Atoms in Magnetic and Optical Trap

S. Pradhan, Laser and Plasma Technology Division, Bhabha Atomic Research Centre, , Mumbai.

The winners got cash award of Rs 2,500 each and certificate. The awards were given by Prof. Dr Dhanasekharan, Anna University, on 20-12-07 during concluding session of NLS-7. M/s Laser Spectra Services, Bangalore sponsored the award money.

Best Poster awards

In the seventh DAE BRNS National Laser Symposium (NLS-7), there were 269 papers for poster presentation. The papers were grouped into 5 categories. Each category had nearly same number of papers and one paper from each category was selected for award. Following five papers were selected for award by the panel of judges.

1. Comparison of the Properties of Microcrystalline TAG Powder Prepared by Sol-Gel Techniques from Oxides and Nitrates

Humyra Shabir, Bansi Lal, M. Rafat* IIT, Kanpur, *Jamia Milia Islamia, New Delhi

2. Performance Characteristics of Remotely Tunable, High Repetition Rate, Copper Vapor Laser Pumped Single Longitudinal Mode Dye Laser

Sunita Singh, G Sridhar, V.S. Rawat, N. Kawde, AS Rawat, S.K. Mishra, L.M. Gantayet, BARC, Mumbai

3. A Novel Method of Intense keV X Ray Generation from In Situ Produced Silver Clusters Using Ti : Sapphire Laser Pulses

U. Chakravarty, P. A .Naik, R. A. Khan, P. D. Gupta, RRCAT, Indore

4. New Autoionization Resonances of Uranium by Three-Color Resonance Ionization Spectroscopy in Hollow Cathode Discharge Tube

M. L. Shah, Vas Dev, B. M. Suri, BARC, Mumbai

5. Effect of He-Ne Laser Irradiation on Hair Follicle Growth in Testosterone Treated Mice Investigated with Optical Coherence Tomography and Histology.

Sunita Shukla, Yogesh Verma, Khageswar Sahu, K. Divakar Rao, Alok Dube, Pradeep Kumar Gupta, RRCAT, Indore

The authors of each winner poster were given Rs 1500/- cash prize money and a certificate. Authors or their representatives received the awards and certificates from Prof. B. P. Singh, IIT, Mumbai, on 20-12-07 during concluding session of NLS-7. M/s Laser Science, Mumbai sponsored these awards. The cash award includes Prof. Vinay Srinivasan memorial award money.

Report prepared by: S. V. Nakhe, General Secretary II, ILA

Best Thesis and Best Poster Awards ofNational Laser Symposium - 07

43

Indian Laser Association (ILA) conducts

short courses every year on laser related topics

preceding National Laser Symposium for the

benefit of young researchers and professionals

working in the area of laser science and

technology. For the year 2007, ILA planned three

one-day courses preceding seventh DAE-BRNS

National Laser Symposium. These courses were

1) Laser Material Processing, 2) Fiber Optics and

Applications to Sensors and 3) Electronic

Instrumentation in Laser Laboratories and these th th thwere conducted on 14 , 15 and 16 December

2007, respectively.

The course on Laser Material processing

was jointly coordinated by Dr. S. M. Oak, Head,

Solid State Laser Division, RRCAT, Indore and

Dr. C. J. Panchal, M. S. University of Baroda,

Vadodara. Lectures covering different aspects of

laser material processing and its industrial

applications were delivered by Shri R. Kaul and

Shri B. N. Upadhyay from RRCAT. Practical

demonstration of laser based systems for 3-

dimensional mapping & scribing, especially those

used in diamond industry, was conducted by M/S.

Sahajanand Laser Systems as a part of this course.

A compact sealed off CO laser was also 2

demonstrated. There were many participants from

industry among around 40 participants for this

course.

The course on Fiber Optics and Applications

to Sensors was coordinated by Prof. V. P. N.

Nampoori, CUSAT, Cochin. First he explained

relevant basics of fiber optics and then he covered

various sensor applications using fiber optics. In

his presentation Prof. V. P. N. Nampoori cited

interesting historical references and also showed

very informative short movie clippings prepared

at CUSAT. The course was very well received by

all the 45 participants for this course.

The course on Electronic Instrumentation in

Laser Laboratories was coordinated Shri C.P.

Navathe, Head, Laser Electronics Support

Section, RRCAT, Indore. This course was

delivered by seven lecturers covering various

electronic instrumentation techniques. The topics

included were laser power and energy meters

(Shri Ashutosh Sharma), signal detection in

presence of noise (Shri R. Arya), optical spectrum

analyser (Shri P.Saxena) and instruments for

recording fast optical events (Shri M. S. Ansari).

The course also covered special aspects of

electronic systems required in laser laboratories

namely high voltage and fast pulse generators

(Shri C. P. Navathe), PC interfacing techniques

(Shri Viraj Bhanage) and electromagnetic

interference issues in laser laboratories (Shri S. V.

Nakhe). All the speakers for this course were from

RRCAT, Indore. This course attracted maximum

number ( 55 ) of participants.

Each course participant was provided a CD

containing all presentations made by all the

lecturers and related information of the particular

course. This will be a very useful reference for the

participants. Participants expressed their

satisfaction over the organization of the courses

and fruitful and informative discussions with

lecturers. Certificate of participation was given to

each registered participant by ILA.

Infrastructure facilities and volunteers'

support were made available by M. S. University

of Baroda, Vadodara for the organization of these

ILA short courses. Guidance from ILA President

Dr. P. D. Gupta, RRCAT, Indore at different stages

of the course planning and execution played a key

role in successful organization of these short

courses.

Report prepared by:

S. V. Nakhe, General Secretary II, ILA

thILA Short Courses Preceding 7 DAE-BRNS National Laser Symposium 2007

44

ILA Reporrts

Indian Laser Association

Receipt and Payment Account for the period 01-04-2006 to 31-03-2007

Receipts Amount (Rs.) Payments Amount (Rs.)

Opening Balance Postage and Telegram Expenses 5710.00

of Kiran, I.L.A. and N.L.S

Cash In hand 4510.00 ILA Course -Honorarium 6500.00

Cash at Bank 430165.95 ILA Course Expenditure 12054.00

Fixed Deposits 483967.00 Symposium Expenditure 146624.00

Exhibition Expenditure 68604.00

Interest on Savings Bank A/c 13896.00 Best Thesis and Poster Awards 17500.00

Interest on Fixed Deposits 31321.00 Kiran Magazine Printing 111267.00

Life Membership Fees 37210.00 Web Domain name 684.00

Student Membership Fees 8250.00 Audit Fees 1500.00

Short Term Course Fees 34450.00 Tax Deducted at Source by Bank 3382.0

National Laser 54538.00 Bank Charges 3765.00

Symposium Exhibition

Contribution

Best Poster award 17500.00 Closing Balance

contribution

NLS Bag Sponsorship 45000.00 Cash In hand 11120.00

ILA Exhibition 327200.00 Cash at Bank 199297.95

Fixed Deposits 900000.00

Grand Total 1488007.95 Grand Total 1488007.95

sd/-Amul Rangnekar

(Proprietor)

sd/-Treasurer

sd/-President

sd/-Secretary

Date: 13/9/2007

Place: Indore

For Amul Rangnekar & Co.

Chartered Accountants

45

The seventh DAE-BRNS National Laser

Symposium (NLS-7) was held at MS University

of Baroda, Vadodara, between December 17-20,

2007. This symposium was sponsored by “The

Board of Research in Nuclear Sciences” (BRNS)

and organized in collaboration with the Indian

Laser Association (ILA). One of the main aims of

BRNS in organizing these symposia is to initiate

research activities between DAE units and

universities. The symposium, which is now an

established annual scientific event, gives the laser

community all over the country the opportunity to

meet and interact.

The symposium was inaugurated by Dr.

Manoj Soni, Vice Chancellor, M.S University of

Baroda. In his inaugural speech Dr. Manoj Soni

welcomed all the participants. The chief Guest of

the symposium was Dr. C.K.N Patel, a well

known name in laser community being inventor

of CO laser. Dr. C.K.N Patel gave the “keynote 2

address”. The topic of his presentation was

“Laser Based Techniques for the Trace Gas

Detection for Industrial, Environmental, Medical,

Defense and Counter Terrorism Applications”. In

his lecture Dr. C.K.N Patel presented various ultra

sensitive techniques to detect chemical warfare

agents, explosives and toxic industrial gases at

ppb or ppt level. After inaugural function, an

exhibition of laser related products organized by

the Indian Laser Association (ILA) was

inaugurated by Dr. C.K.N Patel along with Dr.

Manoj Soni. In total, more than 30 companies

participated in the exhibition, which continued on

all the days of symposium.

The technical sessions on the first three days

comprised of invited talks covering the recent

work carried out in various areas of Lasers and

their applications. This included sessions on

Laser Plasma Interactions (Dr. P.D Gupta,

RRCAT); Physics and Technology of lasers (Dr.

Anil Kumar, LASTEC, Delhi and Dr. S. Kundu,

BARC, Mumbai); Laser Spectroscopy (Dr.

Wilfried Nortershauser, University Mainz,

Germany and Prof. S. Umapathy, IISC,

Bangalore); Laser Biomedical Applications

(Prof. Kankan Bhattacharyya, IACS, Kolkata, Dr.

S.K Mohanty, Beckman Laser Institute,

University of California and Prof. Michel

Manfait, France); Nonlinear Optics (Dr. B.P

Singh, IIT, Mumbai and Dr. C.S Unnikrishnan,

TIFR, Mumbai and Prof. Hema Ramachandaran,

RRI, Bangalore); Quantum Optics (Prof. R.

Simon, Matscience, Chennai); Optics (Prof. M.P

Kottiyal, IIT Madras); Laser Photochemistry (Dr.

S.K. Sarkar, BARC, Mumbai and Dr. A.K Nayak,

BARC, Mumbai); Lasers in Nuclear Science and

Technology (Dr. Sailesh Kumar, BARC, Mumbai

and Shri Sendhil Raja, RRCAT, Indore); Laser

Application in Space and Communication (Dr.

A.S Kiran Kumar, SAC, Ahmedabad and Dr. S.M

Joshi, MS University, Baroda).

A special issue of “KIRAN”, the Bulletin of

Indian Laser Association, consisting of extended

abstracts of the invited talks presented in the

technical sessions was brought out at the time of

symposium and distributed to the participants.

All the contributed papers at NLS-7, totaling

273, were presented in the Poster Sessions on the

first three days of the symposium. All these papers

have been compiled in a CD, which was

distributed to all the participants at the time of

registration on the first day.

On the second day of the symposium, a

session in the evening was devoted to ILA

activities. A brief overview of ILA activities was

given by Dr. P.D Gupta, ILA President which was

then followed by description of general activities

by Shri S.V Nakhe, ILA General Secretary-II,

Accounts by Shri H.S Vora, ILA Treasurer, ILA

bulletin “KIRAN” by Dr. L.M Kukreja and ILA

Web activities by Dr. P.A Naik and Shri Rajiv Jain.

The first session of the last day of the

symposium was devoted to the thesis

presentations, A total of seven theses were

Report on National Laser Symposium-07 (NLS-07)MS University of Baroda, Vadodara, December 17-20, 2007

46

presented. A panel of judges was formed to assess

the thesis work in terms of quality, quantity and its

presentation by candidate and select for the award

for the best thesis.

This was followed by the concluding

session, which was co-organized by the ILA. Shri

J.K Mittal, Convener NLS-7, gave a brief review

of the symposium. Shri S.V Nakhe, General

Secretary-II, ILA, addressed the audience and

presented the details of the activities and

achievements of ILA. During concluding session

“Best Thesis” and “Best Poster” awards were

given by Dr. B.P Singh of IIT, Mumbai. The best

thesis awards were given to Shri Saptarishi

Chaudhuri (TIFR, Mumbai), Shri Sunil Verma,

Shri Jogy George (RRCAT, Indore) and Shri S.

Pradhan (BARC, Mumbai). Best poster awards

were given to Ms. Humyra Shabir (Indian

Institute of Technology, Kanpur), Smt. Sunita

Singh and M. L. Shah (BARC, Mumbai), Shri U.

Chakravarty and Smt. Sunita Shukla (RRCAT,

Indore).

Two cultural programs were arranged during

the symposium. On the first day Gujarati folk

dances were presented by Sanskruti Group,

Vadodara and on second day local artists of MS

University and Sanskruti group presented a

variety of cultural programs. Both the programs

were highly appreciated by the delegates.

As in earlier years, the response to the

symposium was overwhelming. About 280 papers

were received, all of which were reviewed and

273 papers were accepted for poster presentation.

There were 415 registered participants, including

166 students.

On the whole, the symposium seems to have

achieved its aim of bringing together researchers

and students of Laser community on one platform

and acted as a catalyst for increased interaction

and cooperation among delegates.

Manoj Kumar

Secretary NLS-7

J.K Mittal

Convener, NLS-7Raja Ramanna Centre for Advanced Technology,

Indore - 452 013.

Forthcoming Issue of KIRAN

We have tentatively planned the following theme area of next issue of ‘Kiran’:

August 2008 : Lasers in Materials Science

"Feature Articles" and news items for "From Indian Laser Laboratories" are invited for

publication in this issue of KIRAN. Kindly send the write-ups to :

Dr. L.M.Kukreja

Editor, KIRAN

Raja Ramanna Centre for Advanced Technology, Indore-452013.

E-mail : kukreja@cat.ernet.in

47

The Indian Laser Association (ILA)

executive committee has been considering

possible ways of enhancing the interaction

between laser experts and students at smaller

universities and colleges. A proposal that has

emerged from these deliberations is to facilitate

and encourage visit of ILA members, well

recognized for their expertise in areas of laser

physics and technology or on applications of

lasers in various areas, to universities or colleges

close to their work place (within approximately

150 km). Apart from interacting with the faculty

and staff, the expert, who may volunteer for such

visits, will be expected to give 2/3 lectures per day

at tutorial level on topics of interest to the host

institute. This proposal was discussed in the last

ILA General Body Meeting held on Dec 18, 2007

at Vadodara during the DAE-BRNS National

Laser Symposium 7 and was approved. The

operative parts of the scheme are as follows.

1. University or college interested in

organizing a visit of a laser scientist with

work place close to the host institute may

take consent of the concerned expert and

send a proposal to Gen. Secretary-II, ILA.

Alternatively the expert may also contact the

university or college and have them send a

proposal to Gen Secretary- II, ILA.

2. ILA members in the grades of Reader or

above in the university system and

equivalent grades in national laboratories

would qualify for giving lectures under this

scheme.

3. The local hospitality (lodging and boarding)

for the lecturer are to be provided by the host

college / university. ILA would reimburse

round trip travel support (by train up to II

AC/ taxi/bus, NO AIR TRAVEL) and may

also partially contribute towards local

hospitality expenses in case the host institute

is unable to totally cover this. TOTAL

SUPPORT FROM ILA FOR A VISIT

SHOULD NOT EXCEED Rs.2500. Two

lecturers covering different aspects may also

make a joint visit.

4. After the visit, the visiting scientist should

submit the travel bills to Treasurer, ILA

along with a brief report on the visit.

Proforma for making a visit proposal, and

submission of report and reimbursement

claim are available on ILA website. The

travel bills will be reimbursed through an

account payee cheque / DD / or electronic

transfer issued by ILA.

5. ILA plans to support up to 30 visits per year

to begin with. ILA will make attempts to

ensure that the visits arising from this

program are geographically distributed

through out the country.

6. A list of the visits will be put on the ILA

website and also published in Kiran. ILA

members meeting the aforementioned

criterion are requested to volunteer their

services under this scheme to make this

activity fruitful, cost effective and

widespread.

Contact Addresses:

Mr. S.V. Nakhe

Gen. Secretary-II, ILA

C-1 block, LSED, RRCAT,

P.O. CAT, INDORE - 452 013.

Ph. 0731-2442409, Fax: 0731-2442400

Email: nakhe@cat.ernet.in

Mr. H.S. Vora

Treasurer, ILA

C-1 block, LSED, RRCAT,

P.O. CAT, INDORE - 452 013.

Ph. 0731-2442401, Fax: 0731-2442400

Email: vora@cat.ernet.in

Website : http://www.ila.org.in

ILA Lectures SchemeAnnouncements

48

Proforma for Approval to be Submitted by the Host Institute / Lecturer

1. Name of the lecturer : _________________________________________________________________

Affiliation : ___________________________ Designation : __________________________________

Phone : _______________________________ Email : ______________________________________

2. Institute to be visited : _________________________________________________________________

3. Address of the institute : _______________________________________________________________

4. Contact person at the institute visited.

Name : _______________________________ Designation : __________________________________

Phone : _______________________________ Email : ______________________________________

5. Expected travel expenditure :

6. Proposed plan of visit :

Lecture no. Date Time Topics to be covered

Please send this to:

Mr. S.V. Nakhe

Gen. Secretary-II, ILA

C-1 block, LSED, RRCAT,

P.O. CAT, INDORE - 452 013.

Ph. 0731-2442409, Fax: 0731-2442400

Email: nakhe@cat.ernet.in

I have incurred following expenditure on lectures delivered under ILA Lectures Scheme at (Institute visited):

Travel expenditure : Rs. _________________ (Mode of travel : _________________ )

Other expenditure : Rs. _________________ (Indicate if any)

Total expenditure : Rs. _________________

Please reimburse the amount by cheque / electronic transfer

Drawn in favor of ____________________________________________________________________

Payable at ____________________________________________________________________

Bank details ____________________________________________________________________

Account number : ____________________________________________________________________

I have not claimed this expenditure from any other source.

Pre-receipt for the Reimbursement of

Expenditure Incurred on ILA Lectures

I have received Rs. _____________________________________________ by cheque / DD / electronic

transfer from Indian Laser Association towards reimbursement of expenditure incurred on the lectures delivered

under ILA Lectures Scheme.

Signature : Date :

Name : __________________________________________________________________________

Address : __________________________________________________________________________

Please send this form along with feedback form on lectures to :

Mr. H. S. Vora

Treasurer, ILA

C-1 block, LSED, RRCAT,

P.O. CAT, INDORE - 452 013.

Ph. 0731-2442401, Fax: 0731-2442400

Email: vora@cat.ernet.in

49

Request for the Reimbursement of Expenditure Incurred on ILA Lectures

1. Name of the lecturer:

Affiliation : ________________________ Designation: _____________________________

Phone :____________________________E-mail : _________________________________

2. Institute visited : ____________________________________________________________

3. Contact person at the institute visited.

Name : ___________________________ Designation : _____________________________

Phone : ___________________________ Email : __________________________________

4. General comments :__________________________________________________________

a. Background of participants : B.Sc., M.Sc, B.E. etc. _____________________________

b. Response of participants : _____________________________

c. Facilities at the visit place : _____________________________

d. Support by authorities at the institute visited : _____________________________

e. Any other specific comments : _____________________________

5. Details of the lectures delivered.

Lecture no. Date Time Topics covered No. of participants

50

Feedback form to be given by the Lecturer

51

Full Name :

Address for correspondence :

PIN Code

Tel. No. Fax No.

E-mail Address :

Other Address (Res./Office) :

PIN Code

Tel. No. Fax No.

Date of Birth :

Academic Qualifications :and Award / Honours received

Present Position :

Fields of Specialization :

Type of membership requested : Life (Fee : Rs. 1000/-) / Corporate (Fee : Rs. 10000/-) / Student (Fee : Rs. 250/-)

Any particular field in which : Writing articles / Giving popular talks / Local organization / Othersyou would like to contribute (Please Specify)to ILA activities

Membership Payment : Cheque# / Bank Draft No.

DATE SIGNATURE

Send completed application form along with payment to : General Secretary II, ILA,R&D Block C-1,Raja Ramanna Centre for Advanced Technology,PO : CAT, INDORE - 452 013 (M.P.)E-mail : nakhe@cat.ernet.in

# Make Cheque / Draft payable to Indian Laser Association. Drafts should be payable at Indore.# For outstation cheque please add Rs. 35 upto 1000/- rupees and additional Rs. 4.5 per extra thousand rupees for bank charges. Combined payment is acceptable.

FOR ILA OFFICE

Membership type and No. :

Membership Receipt No. :

Any other remarks : (General Secretary II)

MEMBERSHIP FORM

INDIAN LASER ASSOCIATION

Over the past two years, the ILA website has established its identity and its visibility has increased many

folds. The site is now recognized by almost all search engines.

ILA Website (http://www.ila.org.in)

Status Report

We have a big share of dedicated visitors,

which comprises 62% of our total visitors who

visited the site either by direct URL or have already

bookmarked our site address. 33% visitors came to

our site through search engines, mostly through

Google search. Rest of the hits were redirection

from other websites.

Every year, at the time of NLS, the website is

extensively used for information dissemination

during and after the NLS. The same was true this

year for NLS-07 held at Vadodara. The activity on

website for each NLS starts from June every year,

with the first announcement of the forthcoming

NLS. We shall make the announcement of the next

NLS as soon as it is finalized.

Details of the new “ILA Lectures Scheme”

have been posted on the website

“Feedjit” added last year was appreciated by

the users. Moving the cursor on the dots gives

location of visitor. This is linked with the Google

Map and one can pin point the city of the visitor.

The ILA website is an asset for all its members and we urge all to make best use of the power of web

technology and increase your participation in making it more useful.

Quarterly variation for last ten quarters

(Q10 is from Oct'07 to Dec'07).

Rajiv Jain

Webmaster, ILA Website

Prasad Naik

Chairman, ILA Web Committee

Recent Visitors

is a publication of Indian Laser Association (ILA)

For circulation among ILA members only.(Not for sale)

Printed by : Rohit Offset Pvt. Ltd. Indore. 2422201-02

Dr. C. K. N. Patel lighting lamp to mark inauguration thof 7 DAE-BRNS National Laser Symposium.

Dr. C. K. N. Patel inaugurating ILA Exhibition during National Laser Symposium - 07