Time-Resolved X-ray Absorption Spectroscopy of Warm Dense Matter J.W. Lee 1,2,6, L.J. Bae 1,2, K. Engelhorn 3, B. Barbel 3, P. Heimann 4, Y. Ping 5, A. Fernandez 5, M.A. Beckwith 5, X. Geng 6, Y. Lee 6, D.E. Kim 6, and B.I. Cho 1,2 1 Dept. of Physics & Photon Science, GIST 2 Center for Relativistic Laser Science, IBS 3 ALS, LBNL 4 LCLS, SLAC 5 LLNL 6 MPK Center for Attosecond Science, Dept. of Physics, POSTECH

2 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

3 Warm Dense Matter is defined by temperature of 1~100 eV & near solid densities Warm Dense Matter [WDM] High temperature (1-100 eV) & Strongly coupled ions ( Γ ii >1) Warm Dense Matter lies between 4 states & covers many physics issues ρ - T diagram WDM is important to solve un-known ionic, heat, electronic, optical properties. ▶ ICF, Astrophysics, High power Laser-Matter interaction

4 Electron mean free path in WDM seems to be not the same as ambient conditions Electron mean free path in WDM seems to be not the same as ambient conditions Using TR-XAS technique, time delays of backside heating could be determined If Au thickness < mfp, No delay ~10 6 m/s [Fermi velocity] If Au thickness > mfp, time delay ~10 4 m/s [Diffusion velocity] Electron MPF of Au at E F : 117nm (under ambient condition) J. Hohlfeld et al, Chem. Phys (2000) Optical pump-probe study indicated the MPF in WDM condition may not be the same. T.Ogitsu et al, HEDP (2012) Experimental Concept AuCuAuCu fs-laser pump X-ray probe within Ballistic range above Ballistic range

5 BL is specially designed to perform fs-laser pump - soft x-ray probe experiment Lawrence Berkeley National Laboratory Electron energy = 1.5 GeV ~ 280 bunches in Mutil-mode Allowing pseudo single bunch mode Advance Light Source Pump Pulse (~150 fs) 1.5 – 3.0 J/cm nm (doubling) Ti:S fs-Laser Spectral resolution 1 eV 1000 lines/mm Pt coating grating VLS J.Feng, Appl. Phys. Lett (2010) Probe Pulse (~70ps) 900 – 1,000 eV near Cu L-edge (~ 930 eV) Soft X-ray Temporal resolution 2 ps Sweep time 60 ps Streak Camera J. Feng et al, APL (2010) BL of ALS, LBNL Streak Camera Target chamber Storage Ring fs-Laser for pump Streak Camera

6 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 B. I. Cho et al, PRL (2011) Cu-L 3 L2L2 t=0 Red-shift Time Energy

7 Heating through 50 nm of WDAu takes 2ps more than 20 nm Au20/Cu70 Absorption Maximum red-shift 2 Au20/Cu (= Bare-Cu) 4 Au50/Cu (2 ps later) Cu-L 3 Cu-L 2 Cu-L 3 L2L2 t=0 Au50/Cu70 Absorption t=0 Time Energy Time Energy 0ps 2ps 4ps 6ps 8ps 10ps 0ps 2ps 4ps 6ps 8ps 10ps Au20/Cu Au50/Cu MAX

8 Diffusion seems to play important role for electron transport through 50nm Maximum T e ~ ps Velocity of electron ~ 10 6 m/s Fermi velocity Within Mean Free Path Above Mean Free Path ~ ps ~ 10 4 m/s Diffusion velocity Temporal evolution of electric temperature Au20-Cu70Au50-Cu70 Ambient condition WDM condition No Ballistic

9 fs-LASER 5-pass amplifier system (10 Hz) 45 fs pulse duration ~10 mJ/pulse → HHG 1-10 J/cm 2 → Pump HHG Ar/He/Ne Gas pulse Jet 300 shots/min Scanning eV EUV absorption spectroscopy technique could be used to study femtosecond dynamics in WDM fs-laser Pump-HHG probe Especially, hot electron – cold electron thermal equilibrium dynamics Set-up for fs-pump & HHG MPK, POSTECH Ar HHG spectrum

10 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. MPF Au(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. MPF Au(WDM) < 50 nm  HHG source could be used to study femtosecond dynamics in WDM

11 Acknowledgement  This work is supported by Max Planck POSTECH/KOREA Research Initiative Program National Research Foundation (NRF) IBS Center for Relativistic Laser Science