Schlossberg - Lasers and Optics - Spring Review 2012

1 DISTRIBUTION A: Approved for public release; distribution is unlimited. 9 March 2012

Integrity Service Excellence

Howard Schlossberg

Program Manager

AFOSR/RSE

Air Force Research Laboratory

Lasers and Optics

07 MAR 2012

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DISTRIBUTION A: Approved for public release; distribution is unlimited.

2012 AFOSR SPRING REVIEW 2301A PORTFOLIO OVERVIEW

NAME: Dr. Howard Schlossberg

BRIEF DESCRIPTION OF PORTFOLIO:

RESEARCH IN LASERS, OPTICS, AND THEIR APPLICATIONS

LIST SUB-AREAS IN PORTFOLIO:

- LASERS

- NON-LINEAR OPTICS

- LASER-MATTER INTERACTIONS

- MICRO-SYSTEMS

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Anthony E. Siegman 1931 - 2011

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•Invention of Unstable Resonator – 1965

•Keeper of the Modes

•Invention of M2 - 1990

•Ultrashort Pulse Measurements

Tony Wrote the Book on

Lasers

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LASERS

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• High Average Power Solid-State Lasers • Ceramic Laser Solid-State Materials

• Fiber Lasers

• Thin Disk Semiconductor Lasers

• X-PALS

• Modest Power Lasers • Mid-Infrared Semiconductor Lasers

• Mid-Infrared Fiber Lasers

• Nonlinear Optics • Nonlinear Frequency Conversion

• Ultrashort Pulses

• Extreme Light

• High Harmonic Generation

• Mid-and Long Wave Frequency Combs

• X-Ray Imaging

• Micromachining

• Microplasma Arrays • Specialized Lighting

• Plasma chemistry

• Plasma transistor

• RF modulation, protection (DARPA)

Portfolio Summary (Detail)

To Dr. Parra

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• Ceramic Solid-State Laser Materials • Spatially Varying Index and Doping Concentration

• Non-Isotropic hosts

• Fiber Lasers

• Ultra-short, Ultra-Intense Pulses • Matter Interactions, Propagation, X-Ray Beams

• Integrate with HPL JTO Programs

AFOSR Study of 6.1 Opportunities in High

Energy and High Power Lasers

High Energy Solid-State, and Some Gas, Lasers Today

are an Exercise in Mode Conversion

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AGENDA

• Ceramic Solid-State Lasers

• X-Pals, Three Level Lasers

• Photonic Bandgap Gas Lasers

• Ultraviolet Harmonic Lasers

• Multiple Line Pulsed Lasers

Technology Transfer Examples

• Infrared Short Pulse FTIR

• Optical Coherence Tomography (OCT)

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AGENDA









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Ceramic laser gain media offer a number of important

advantages over single crystals and glasses

:

• Ceramic media can be fabricated with arbitrary shapes and size.

• Ceramics are well suited to produce composite gain media,

consisting e.g. of parts with different doping levels, or even different

dopants

• Spatially varying doping profiles are relatively easily possible. These

aspects give additional freedom in laser design.

• Significantly higher doping concentration can be achieved without

quenching effects degrading the laser efficiency.

• Some materials, e.g. sesquioxides are very difficult to grow into

single crystals, and much easier to obtain in ceramic form.

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Ceramic Solid-State Laser Materials

Program Examples

• Ikesue (JTO, Dr. Caster) – Processing, diagnostics

– Navy does characterization, lasing (Shori)

• Ballato - Clemson (JTO, Dr Sayir)

– Sesquioxides

• Byer – Stanford (JTO, AFOSR)

– Nd, Yb, Tm doped ceramics, Tm fibers

– Works with U. Central Florida (Gaume)

• Wu – Alfred University (AFOSR YIP)

– Yb doped Sr5(PO4)3F (Yb:S-FAP)

• Excellent properties as laser host

• Prototype uniaxial material

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AFOSR Sponsored Ceramic Research Meeting in Nagoya

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AGENDA









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There is no requirement that the

pumping frequency be much higher

than the frequency emitted as long as

the difference in frequency is much

greater than kT/h, which can assure

the possibility of negative

temperatures.

Schawlow and Townes, Phys. Rev.

112, 1940 (1958).

DPALS (Cesium)

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4 5 6 6 7

0

1

10

12

14

62P

62S

X2

En

erg

y (

10

3 c

m-1

)

Interatomic Distance (Å)

B2

Cs-Ar

Continuous tunability between 4, 3, and 2 level systems

XPALS SYSTEM: Cs-Ar

~837 nm 852.1 nm

Δε

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• The extracted decay constants from laser

excitation spectra yield transition region

slope of -3/2 kT

• ~0.7 kT is a critical value of the energy

separation between adjacent laser levels

• 4 level laser system collapses in a kT

interval of ~ 2 meV

XPALS SUMMARY

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AGENDA









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PHOTONIC BANDGAP GAS LASERS

•Diode-pumped gas laser

•Long interaction length allows small absorption

•Enhanced efficiency possible through V-V collisions

•Large mode area or coherent coupling possible •Corwin - Kansas State U

• U. New Mexico

•University of Bath

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3.113 3.114 3.1150

100

200

300

400

500

600

3.171 3.172 3.173

Sp

ectr

al In

ten

sit

y (

arb

. u

nit

s)

Wavelength (m)

Actual Wavelengths:

3114.6 nm, R(11)

3172.4 nm, P(13)

C2H2 Pressure = 111 torr

Herman, J. Chem. Ref. Data 32, (2003).

C2H2 Laser Spectrum and Transitions

C H C H

C H C H

ν1

ν3

v1+v3

00000

Energy states

v4

v5

v2

v3

v1

~1.5

m

~ 3

.8

m

8 m

13 m

~ 3

.1

m

~ 3

.8

m

1.7 m

Potential Lasing States

Vibrational ground state

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AGENDA









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T. Carmon, Univ. Michigan Objective: Continuous-in-Time Micro-Emitter at the Extreme UV

Concept:

1) Nonlinear medium

Xenon gas

2) Optical Enhancement by

IR recirculating in a micro-resonator

Local enhancement by metal (Orange)

Compact cw telecom source, no meter-scaled pulsed lasers

3) Indications for High Harmonics

UV detection with an optical spectrum analyzer

Free Electron detection via current monitoring between electrodes

XUV - e

Xe +

UV

- e

Xe +

- e

Xe + Xe +

Compact CW IR

Laser pump

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Tal Carmon, Univ. Michigan Accomplishments: continuous 4th-Harmonic Generation

Experimentally Demonstrated:

–UV 4th-harmonic generation [Opt. Exp. 2011]

– Laser emission with incoherent pumping [Adv. Mater. 2011]

–HyperRaman emission (two-photon-excited analog of Raman) [Appl. Phys. Lett. 2012, accepted]

•Theoretically analyzed:

–An atom-plasmon-resonator system [New J. Phys., To be submitted]

UV Extreme UV

Th

is y

ea

r

3rd Harmonics & 3rd-order sum-frequency

generation (separately measured during

different experiments, Nature Phys. 2007)

Papers are in collaboration with Cohen, Bartal (Technion), Jarrahi (U of M), Rotschild & Baldo (MIT)

Past

resu

lts

Continuous-in-time pump, 2nd-, 3rd-, & 4th-

harmonics emission. Opt. Exp. 2011

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AGENDA









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• Pulse synthesis with wavelength and coherent beam combining integrated into single setup

– Wavelength beam combining controls frequencies

– Coherent beam combining is implemented with feedback from single-phase sensitive metric

• Advantages

– Scalability

– Reconfigurability

– Large pulse energies, high repetition rates, short optical pulses

– Pulse generation in laser systems, or spectral regions where difficult

Laser Locking for Short Pulse Generation

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Laser Locking

• Feedback is based on single phase sensitive metric

– Allows control of large arrays!

• Stochastic parallel gradient descent algorithm is used for feedback

– Determine performance metric and apply random changes to all inputs

– Update parameters with stochastic gradient

– Vary current to laser arrays to cause phase shift from thermally induced index of refraction change

n

j

nn

j

n

j

n

j uJuu 1

Individual phase Single metric

measurement measurement

Feedback

f1, fc

f2, fc

fn, fc

f1 f2fn

Feedback

f1, fc

f2, fc

fn, fc

J(f1 f2…fn)

This work

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AGENDA









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Dual-comb FT spectroscopy

GaSe

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AGENDA








• Optical Coherence Tomography

(OCT)

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Optical Coherence Tomography (OCT)

• Invented with AFOSR funding

• Very broad-based optical diagnostic technique.

• Expanded under program to include Doppler and polarization- sensitive OCT.

• Recent breakthroughs in speed – spectral and swept source OCT – and resolution.

• Military examples: – Burn depth measurement. – Blood flow. – Airway damage.

• Civilian spin-off examples: – Eye problems. – Coronary artery disease – Barrett’s Esophagus.

• Over 16 million eye diagnostics in 2010

• Over 50 thousand coronary artery

procedures to date

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Problem: High mortality from smoke

Inhalation Injury

• 27% of Army burn admissions suffer inhalation injuries

• 10 times greater mortality than other burn patients

• No technology for early diagnosis

Solution: OCT imaging enables early detection

Status: Clinical trials proposed for USAISR & BAMC

Airway - normal

Inflammation following smoke

inhalation

Advances in speed of OCT imaging and

unique optical probe design enables high

resolution 3D airway imaging

Intracoronary OCT Artery Wall

Lipid

Calcium

Macrophages

Stent

3D OCT of Human Coronary Artery in vivo

• Next major intracoronary imaging modality

• Identifies plaques before heart attack

• Guide stent intervention

• 3 major companies

• Over 50,000 patients imaged

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Thank you