Choi Ilwoo1,3 , Nam Changhee1,2 Spectral Change of Backscattered Laser Pulse During Laser-Driven Proton Acceleration Lee SUnggeun1,2 , Kim Ijong1,3 , Choi Ilwoo1,3 , Nam Changhee1,2 1Center for Relativistic Laser Science, Institute for Basic Science, Gwangju 500-712, Korea 2Department of Physics and Photon Science, Gwangju Institute of Science and Technology, Gwangju 500-712, Korea 3Advanced Photonics Research Institute, Gwangju Institute of Science and Technology, Gwangju 500-712, Korea

Contents Theoretical background of Ion Acceleration Spectral change during acceleration Experimental setting Result Summary

Laser Proton/Ion Acceleration

RPA Electron is push by enough high intensity laser pulse contemporally Charge separation occurs, and coulomb force is generated between electron layer and ions Ions accelerates

Spectral change during acceleration Electron layer can reflect incident laser pulse Moving layer with relativistic speed occurs relative Doppler effect Reflected light experienced redshift

Experimental Setup

Comparison of before/after beam hitting the target Input spectrum range (750-850 nm) 1 1 2 Red shift range (850nm~) 2

Typical spectrum with various maximum proton energy

Proton Energy vs Redshift Polymer target (1g/cm2 -> 200nc) CP laser X axis : maximum proton energy obtained by TPS Y axis : Spectrum Integration over 900nm

Amount of redshift Changes in Various Condition Polymer target (1g/cm2 -> 200nc) CP laser Diamond-Like Carbon target (2.7g/cm2 -> 500nc) CP laser

Amount of redshift Changes in Various Condition Diamond-Like Carbon target (2.7g/cm2 -> 500nc) CP laser Diamond-Like Carbon target (2.7g/cm2 -> 500nc) LP laser

Summary We have investigated the spectral structure of backscattered laser pulses during the laser proton acceleration performed with a PW laser. We have confirmed that backscattered light experience more Doppler effect compare to the transmitted light. The relation between the spectral structure of reflected laser pulses and proton energy spectra will be clarified with respect to experimental conditions, such as laser and target parameters