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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 .
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