22C13
White light probe system of solid state
irradiated by EUV free electron laser
EUV自由電子レーザー照射固体状態の白色光観測システム	 	 

T.Ohashi，H.Yoneda，D.Baek，F.Sato，R.Kodama1，Y.Inubushi1,2,T.Kumagai1,D.Kimura1，
K.Nakatsuka1，T.Ishikawa2，H.Ohashi2,3，H.Kimura2,3，Y.Senba3，K.Tono2，T.Togashi2,3，
M.Nagasono2，A.Higasiya2，M.Yabashi2
大橋拓司，白大烈，佐藤文哉，兒玉了祐1，犬伏雄一1,2，熊谷泰輔1，木村大亮1，中塚和樹1，
米田仁紀，石川哲也2，大橋治彦2,3，木村洋昭2,3，仙波泰徳3，登野健介2，富樫格2,3，永園充2，東谷篤志2，矢橋牧名2Institute for Laser Science, University of Electro-Communications.
W7, Chofugaoka 1-5-1, Chofu city, Tokyo 182-8585, Japan
電気通信大学レーザー新世代研究センター 〒182-8585 東京都調布市調布ケ丘1−5−1	  西七号館
1

Graduate School of Engineering, Osaka University
Mihogaoka 8-1, Ibaraki, Osaka 567-0047. Japan
大阪大学大学院工学研究科 〒567-0047	  大阪府茨木市美穂ケ丘8−1
2

RIKEN HARIMA INSTITUTE X-ray Free Electron Laser
1-1-1, Kouto, Sayo-cho, Sayo-gun, Hyogo, Japan
独立行政法人理化学研究所	  播磨研究所 XFEL 〒679-5148 兵庫県佐用郡佐用町光都1−1−1
3JASRI
1-1-1, Kouto, Sayo-cho ,Sayo-gun, Hyogo, Japan	  財団法人 高輝度光科学研究センター（JASRI）〒679-5198 兵庫県佐用郡佐用町光都 1−1−1
Recent development of X-ray and EUV free electron laser makes it possible to achieve high density innershell excitation in the condensed matter. Some nonlinear optical phenomena is observed in Japan andEurope facilities. However, these experiments use only single EUV or X-ray laser pulse so that it is very
difficult to understand the detail dynamics. For this purpose femtosecond white light probe system isprepared and EUV-pump and white-light-probe experiments are done in SCSS EUV line. The preliminary
results denote that atomic polarizability dominates electron one just after the illumination of EUV light.

1. Introduction
Extreme Ultraviolet (EUV) interacts with
inner shell electron, because frequency of EUV
is higher than resonant frequency of freeelectron in the metal. Recently high intensity
EUV generated from free electron laser (FEL)
induces some nonlinear optical phenomena [1].
It is considered that high energy shift of theabsorption edge with change of electron energy
level is induced because most of atomic innershell electrons are excited keeping solid density.
However detailed physics is not to understand.
2. System
We prepare EUV-pump white-light-probe
system with the use of ultra-wideband whitelight pulse (Fig.1) synchronized with EUV-Freeelectron laser. As shown Fig.2: white light
generated from 800nm femtosecond laser andFig.1 White pulse profile by streak camera

sapphire crystal irradiate thin film target
evaporated on fused silica at an incidence angleof 60 degrees. White pulse is reflected on thetarget surface. Finally probe light is observedwith a polarization and vertical resolved
spectrometer. Jitter of the probe pulse is about

Table.1 Comparison Drude model at λ=510nm
Cold
γ+20%
ωc2+20％ωc2,γ+20％

Cold
γ+20%
ωc2+20％ωc2,γ+20％

Fig. 2 Experimental system

200fs because of electrical synchronization.
Generated white pulse has group delay of 5ps
between 450nm and 700nm as shown in Fig.1.
The chirped probe pulse is overlapped a
100fs-EUV pulse.
3. Result and discussion
One of the typical observation data is shown inFig.3 We find to change reflection intensityfrom result. Looking after the EUV shot onFig.3, p polarization reflectivity decrease and spolarization reflectivity increase. we observedreflection intensity decrease longer than 550nm,
on the other hand increase shorter less than550nm. This phenomenon cannot explain
carrier increasing with inner shell electron
excitation and rise of temperature to be
explained by the Drude model written
0.3

theoretical Rp/Rs

300

n0.706k2.031

Rp/Rs
0.139

Rp
0.052

Rs
0.370

0.873

1.936

0.114

0.042

0.367

0.644

2.264

0.161

0.064

0.399

0.803
εre2.161
εim0.135ωc2/（ω2+γ2）

0.053
γ/ω

0.392

-3.6252.8684.625

0.620-2.986

3.381

3.986

0.848

-4.713

2.915

5.713

0.510

-4.026

3.472

5.026

0.691

in Formula (1) to be indicative Table.1! = ! − !"Re⋅ εˆ(ω ) ≡ n 2 − k 2Im⋅ εˆ(ω ) ≡ 2nk!ˆ = n̂ 2 = 1+= 1!

i"
Ne 2
1= 1!
! 0#
m! 0 # (# + i$ )# c2
# c2$+i2222(# + $ ) (# + $ ) #(1)4. Conclusion
We are assuming that Reflection intensitychange effect atomic susceptibility instead ofincrease free electrons.

240_Rp/Rs240_p
240_s2500.2

2000.15150EUV	 

0.10.0510050

10nm = 200fs	 

0470

Reflection Intensity [a.u]

Rp/Rs

0.25

0520570
Wavelength [nm]Fig. 3 Au 10.2 nm film target reflection intensitychanged by EUV-FEL. Blue line is Calculate
Rp/Rs. Purple line is actual measured Rs/Rp. Red
dashed line is reflection intensity of p polarization.
Red dashed line is reflection intensity of ppolarization.

[1] H. Yoneda Optics Express. Vol. 17 Issue 26,
pp.23443-23448 (2009)