Time-Resolved X-ray Absorption
Spectroscopy of Warm Dense Matter
J.W. Lee1,2,6, L.J. Bae1,2, K. Engelhorn3, B. Barbel3,
P. Heimann4, Y. Ping5, A. Fernandez5, M.A. Beckwith5,
X. Geng6, Y. Lee6, D.E. Kim6, and B.I. Cho1,2
1Dept.
of Physics & Photon Science, GIST
for Relativistic Laser Science, IBS
3ALS, LBNL
4LCLS, SLAC
5LLNL
6MPK Center for Attosecond Science, Dept. of Physics, POSTECH
2Center
CONTENTS
 Introduction
- Warm Dense Matter, Ballistic range of hot electrons
 Experimental Setup
- Time-Resolved X-ray Absorption Spectroscopy
 Data & Discuss
- X-ray absorption spectrum
- Temporal evolution of electron temperature
- Ballistic motion
 Future Plan
- fs EUV absorption spectroscopy
 Summary
2
Warm Dense Matter is defined by temperature of
1~100 eV & near solid densities
ρ - T diagram
Warm Dense Matter
[WDM]
High temperature (1-100 eV)
&
Strongly coupled ions (Γii>1)
Warm Dense Matter
lies between 4 states &
covers many physics issues
WDM is important to solve un-known ionic, heat, electronic, optical properties.
▶ ICF, Astrophysics, High power Laser-Matter interaction
3
Electron mean free path in WDM seems to be not
the same as ambient conditions
Electron MPF of Au at EF : 117nm (under ambient condition)
J. Hohlfeld et al, Chem. Phys. 251 237 (2000)
Optical pump-probe study indicated the MPF in WDM condition may not be the same.
T.Ogitsu et al, HEDP 8 303 (2012)
Using TR-XAS technique, time delays of backside heating
could be determined
Experimental Concept
Au Cu
Au
Cu
X-ray probe
fs-laser pump
4
within
Ballistic range
If Au thickness < mfp,
No delay
~106 m/s [Fermi velocity]
above
Ballistic range
If Au thickness > mfp,
time delay
~104 m/s [Diffusion velocity]
BL 6.0.2 is specially designed to perform
fs-laser pump - soft x-ray probe experiment
Storage
Ring
Advance Light Source
Lawrence Berkeley National Laboratory
Electron energy = 1.5 GeV
~ 280 bunches in Mutil-mode
Allowing pseudo single bunch mode
Soft X-ray
Ti:S fs-Laser
Probe Pulse (~70ps)
900 – 1,000 eV
near Cu L-edge (~ 930 eV)
Pump Pulse (~150 fs)
1.5 – 3.0 J/cm2
400 nm (doubling)
VLS
Streak Camera
Spectral resolution 1 eV
1000 lines/mm
Pt coating grating
Temporal resolution 2 ps
Sweep time 60 ps
Target chamber
fs-Laser
for pump
Streak
Camera
Streak Camera
J. Feng et al, APL
96 134102 (2010)
Set-up
@ BL 6.0.2 of ALS, LBNL
5
Electron temperature of WDCu can be determined
from X-ray absorption spectrum
Bare-copper L-edge transmission
X-ray streak camera image
High Temp. XAS &
Temperature determination
DOS of Cu &
Fermi distributions
Time
5
1.5
L2
(b)
Red-shift
(d)
DOS
Solid
Liquid
4
1.0
3
DOS
t=0
Absorption cross section [Mb]
Cu-L3
Calculations
300 K
10200 ± 900 K
0.0
920
2
Exp. @ 2 ps
0.5
1
300 K
6000K
10200K
x10
0
930
940
E [eV]
950
960
-10
-5
0
5
10
15
E - Ef [eV]
Energy
B. I. Cho et al, PRL 106 167601 (2011)
6
Heating through 50 nm of WDAu takes
2ps more than 20 nm
250
300
350
400
450
Cu-L3
500
550
600
L2
650
700
750
250
200
150
200
800
850
900
Au50/Cu
10ps
10ps
8ps
8ps
500
450
Time
400
350
300
t=0
Au20/Cu
6ps
600
550
6ps
4ps
4ps
700
650
Au20/Cu70 Absorption
MAX
Energy
250
300
350
400
450
500
550
600
650
700
750
800
850
900
2ps
MAX
2ps
250
200
150
200
Cu-L2
0ps
Cu-L3
0ps
7
Au50/Cu70 Absorption
700
650
600
550
500
450
Time
400
350
300
t=0
Energy
Maximum red-shift
2 ps @ Au20/Cu (= Bare-Cu)
4 ps @ Au50/Cu (2 ps later)
Diffusion seems to play important role for
electron transport through 50nm
Au20-Cu70
Au50-Cu70
Temporal evolution of electric temperature
Maximum Te
Velocity of electron
~10900 K @ 0 ps
~ 106 m/s Fermi velocity
Within Mean Free Path
~ 104 m/s Diffusion velocity
Above Mean Free Path
~8900 K @ 2 ps
Ambient
condition
8
100 nm
= 0.1 ps
106 m/s
WDM
condition
30 nm
= 1.5 × 104 m/s
2 ps
No Ballistic
EUV absorption spectroscopy technique could be used
to study femtosecond dynamics in WDM
fs-laser Pump-HHG probe
fs-LASER
5-pass amplifier system (10 Hz)
45 fs pulse duration
~10 mJ/pulse → HHG
1-10 J/cm2 → Pump
Set-up for fs-pump & HHG probe @ MPK, POSTECH
HHG
150
200
250
300
350
400
450
500
550
600
650
700
750
Ar/He/Ne Gas pulse Jet
300 shots/min
Scanning 50-70 eV
550
500
450
400
350
100
600
Especially,
850
800
750
700
650
hot electron – cold electron
thermal equilibrium dynamics
9
Ar HHG spectrum
Summary
 WDM refer states which have both plasma temperature & near
solid density.
 Electron MPF in WDM is related to various transport properties
(thermal and electrical conductivities), but may not be the same
with ambient ones. ex. MPFAu(cold) : ~ 117 nm
 Time-resolved X-ray Absorption Spectroscopy has capability to
determined the electronic temperature and its temporal
evolution.
 Diffusion seems to play important role for electron transport
through 50 nm Gold in WDM conditions. MPFAu(WDM) < 50 nm
 HHG source could be used to study femtosecond dynamics in
WDM
10
Acknowledgement
 This work is supported by
National Research Foundation (NRF)
IBS Center for Relativistic Laser Science
Max Planck POSTECH/KOREA Research
Initiative Program
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