Improved application beam line and recent experiments on the NIJI-IV DUV/VUV FEL

H. Ogawa, K. Yamada, N. Sei, R. Kuroda,K. Yagi-Watanabe,M. Yasumoto, T. Ohdaira, R.Suzuki

National Institute of Advanced Industrial Science and Technology (AIST),Tsukuba, Japan

CONTENTS

● Compact NIJI-IV FEL system

● Improvement of optical cavity

● Cavity-mirror degradation

● NIJI-IV DUV FEL for PEEM application

● Summary

NIJI-IV FEL

ETLOK-II ETLOK-III

Total length [m] 6.288 3.55Magnetic periodUndulator section [mm] 72 200Dispersive section[mm] 216 720Number of period Nu 42×2 7×2Deflection factor K <2.29 <10.04Wavelength [µm] 0.198-0.595 (0.4-10)

UV/VUV

IR

UV/VUV FEL

IR FEL10

Lasing in the NIJI-IV FEL

190 195 200 205 210 215 220 22502468

10121416182022

original loss

degraded-cavity loss(exposure:250 mAh)

degraded-cavity loss(exposure:150 mAh)

CAV

ITY

LO

SS,

PEAK

GAI

N (%

)

WAVELENGTH (nm)

1.8

1.6

1.4

1.2

previous gain with old chambers

present gain with low-impedance chambers

0

original loss

0.2

0.4

0.6

0.8

1.0

LASE

R IN

TEN

SITY

(arb

. uni

ts)

0

1

2

3

4

5

INTE

NSIT

Y(a

.u.)

FAST SWEEP TIME(ps)0 20 40 60 80

6.7 ps

Lasing down to 198nm (~ 595nm)Line width: 0.07nm

DUV/VUV Beam line for FEL-PEEM(Photoelectron emission microscopy)

An FEL at a wavelength of 202nm emitted from a 6.3-m optical klystron ETLOK-II was transported to the experimental room through air and was reflected by a flat aluminium mirror and focused onto the sample surface.

M1

M2

Optical Klystron

BM3

BM2

QDQF1UpstreamMirror chamber

PEEM apparatus

Monochrometor

Storage Ring NIJI-IV

DUV FEL

He-Ne laser

Sample

Optical cavity system for DUV/VUV FEL Old system

Slender structure

heavy granite stone(2 ton)

Robust optical cavity sytem

The mirror manipulators were composed of five-axis stages withgimbal mounts containing a high-vacuum mirror chambers each of which has interchangeable two in-vacuum mirrors to extend FEL tuning range.

Resolution: ∆z = 0.1µm , ∆θ=0.8µrad

substrate (SiO2)

SiO2

Al2O3

53layers

150 200 250 300 350 400 450 500 550 600 6500

1

2

3

4

5

UVVUV

Intensity [ a.u. ]

Wavelength [nm]

Ta2O5, TiO2HfO2Al2O3

Degradation of dielectric mirror in the visible and UV regions

The mirror bandwidth was narroweddue to deposition of carbon atoms onto the mirror surface.

initial

previous work

O2 plasma treatment

K.Yamada: NIMA393(1997)

O2 plasma treatment in the visible and UV regions

After treatment

Reduction of carbon contamination after plasma treatment was confirmedby XPS analysis.

K.Yamada Appl. Opt. 34 (1995)

We already demonstrated to TiO2/SiO2, Ta2O5/SiO2, HfO2/SiO2.

1064nm, 10Hz3ω(355nm) 350mJ

Nd:YAG Laser

Frequency conversion unit

SHGTHG

Mode matching lensesN2 gas

Detector

1064nm

355nmDoublingcrystal (BBO)

Mixingcrystal (BBO)

Dye Laser 460-535nm, 40mJ

Ring-down cavity

FEL mirror

Mirror Loss Measurement Cavity ring-down method

GPIB

Computer

Oscilloscope

trigger

193 – 210 nm

⎟⎟⎠

⎞⎜⎜⎝

⎛−=

c

tItIτ

exp)( 0

cLnlc

c2

=τ5 10 15 20 25 30

1E-4

1E-3

0.01

I (a.u.)

time (µs)

Mirror Losscavity decay time

194 196 198 200 202 204 206 208 2100

1

2

3

4

5

6

Mirror Loss (%)

Wavelength (nm)

initial

degraded(exposure:245mAh)

Mirror degradation around 200nm

The mirror bandwidth was narrowed. O2 plasma treatment

Al2O3/SiO2

RF-induced O2 plasma treatment

0 50 100 150 200 250 300

0.2

0.4

0.6

0.8

1.0

1.2

Mirror Loss (%)

Time (sec)

O2 plasma

Mirror

To remove surface carbon contamination,the surface was treated with O2 plasma.

O2 gas : flow rate of 100ml/min

Restoration of degraded mirror

20sec

60Pa The treatment time of at least 20sec isenough to restore the degraded mirror.RF: 13.56MHz, 300W

194 196 198 200 202 204 206 208 2100

1

2

3

4

5

6

Mirror Loss (%)

Wavelength (nm)

initial degraded treated with O

2 plasma

After plasma treatment

initial

degraded(exposure:245mAh)

The narrowing of the mirror bandwidth disappeared and the shape of mirror loss curve was repaired, while the absolute value was still larger.

After O2 plasma treatment

volume degradation through defect formation inside the dielectric layers.thermal annealing treatment

194 196 198 200 202 204 206 208 2100

1

2

3

4

5

6

Mirror Loss (%)

Wavelength (nm)

initial degraded treated with O

2 plasma

annealed at 300 ﾟC

After plasma treatment

initial

degraded(exposure:245mAh)

After thermal annealing treatment

After annealing at 300ﾟC

Degradation was almost restored.To examine the degradation mechanism due to inner defects, we performed positron lifetime experiments.

slow-positron pulsing system

Low-k filmγ ray

γ ray511keV

511keV

pore

BaF2 + PMT

Trigger

Start Stop

e+Substrate

Depth-selective PALS system at AIST

Positron annihilation lifetimes

Measurable pore-size range : mono-vacancy – 100 nm.

Observation depth : surface to ～3μm (E=0.3～30keV).

Depth-selective PALS(Positron Annihilation Lifetime Spectroscopy) system

10 100 1000 10000

Pro

files

10 keV3 keV1 keV

Depth (nm)

pure SiO2

defects

bond-like-type defectsLong-lived component is reduced.

Si O

0 5 10 150

10

20

30

I L(%)

Positron Energy (keV)

initial degraded treated with

plasma and annealing

In the UV and visible regions, the defect was completely repaired with 230-250ﾟC annealing

Result of Positron experiment

initial

degraded

After annealing at 300ﾟC

In the DUV/VUV, annealing should be more higher temperature to repair completely.

NIJI-IV FEL-PEEM (photoelectron emission microscopy) system

DUV FEL

Sample chamber

PEEM

MCP Projective Lens B Intermediate Lens

Objective Lens

Sample

Screen

Projective Lens A

DUV FEL

NIJI-IV DUVFEL was applied to surface observation, in combination with a PEEM system (STAIB Instrumente, type 350). This PEEM system has three sets of electrostatic electronlenses and a micro channel plate (MCP) equipped with a fluorescent screen. By viewing the focused images on the fluorescent screen with a CCD camera, transient phenomena, such as chemical reactions on transition-metal surfaces, can be monitored with video-rate time resolution. Since the spatial resolution of this system is 80 nm and our FEL intensity is large enough to extract sufficient amount of photoelectrons to recognize the surface contrasts within 33.3 msec, we can examine real-time physical and chemical information on transition-metal surfaces in a sub-micron scale.

Magnification 200-2000Field of View 20μm-200μmGuaranteed Resolution 100nmLimited Resolution 80nm

DUV FEL

PEEMSample chamber

CCD

Catalytic CO oxidation (2CO + O2→2CO2) on a Pd(111) surface

Pt(110) 　　 5.5eVPt(110) + CO 5.8eVPt(110) + O 6.5eV

Workfunctionφ

FEL

In case of Pt(110)

e-

e-

e-

Produced CO2 gas desorbs immediately.pure Pd(111) surface Pd(111) + CO

Exposed to CO gasdark surface

２CO＋O2→２CO2

bright surfaceExposed to O2 gas

K.Yamada: FEL Conf. 2004

Expansion of CO domain on a Pd(111) surface

CO （5×10-6 Pa)O2 (4×10-5 Pa)

T = 360K

Exposure

0 sec50µm 20 sec 30 sec

35 sec 60 sec 150 sec

It is supposed that the oxygen play a role in preventing a speed of CO expansion.

Observation of Cs2Te Photocathode

Load-lock system

Cs2Te PhotocathodePEEM objective lens

talk on Wednesdayby Kuroda

Observation is now proceeding

Cs2Te

Te

354nm

200nm

NIJI-IV FEL

Stable optical cavity system was installed for DUV/VUV and IR FEL.

Summary

Degradation in Al2O3/SiO2 mirror was studied around 200nm.The degraded mirror was successfully restored by treatment ofO2 plasma and thermal annealing.

As for FEL application study, a real-time imaging of chemicalreaction was performed with PEEM and Cs2Te photocathodeobservation is now proceeding .