Characterization of short-pulse laser produced fast electrons by using 3-D hybrid particle-in-cell simulations

Understanding of generation and characterization of fast electrons generated in high-intensity, short-pulse laser-target interaction is important for the development of broadband x-ray sources, creation of high energy density plasma and advanced inertial confinement fusion concepts. We have characterized short-pulse laser produced fast electrons by modeling angularly resolved bremsstrahlung with 3D simulations using a hybrid particle-in-cell code, Large Scale Plasmas (LSP). The experiment was performed at UNR using a 50 TW Leopard laser delivering a 15J, 0.35 ps pulse at a peak intensity of 2×10 19 W/cm 2 . The interaction of the laser pulse with a metal foil generates relativistic electrons predominantly by the ponderomotive potential. Subsequently, the transport of the electrons produces angular dependent bremsstrahlung and high energy electrons escape from the target rear. Bremsstrahlung photons and escaped electrons were recorded with two absolutely calibrated differential filter stack spectrometers and a magnet-based electron spectrometer, respectively. The bremsstrahlung measurements were then modeled with 3-D LSP simulations by varying input electron spectrum (T hot ), divergence angle (θ) and electron beam energy (E hot ). Ranges of the electron characteristics for the Leopard laser are deduced by using a chi-square fitting and the electron spectrum measurements. For a 100 μm thick Cu target, the input fast electron parameters are estimated to be T hot =1.0-1.5MeV, θ=~70º and E hot =0.8-1.5J. The slope temperature inferred from the analysis of the bremsstrahlung agrees with the direct electron measurement. The estimated electron beam energy corresponds to a conversion efficiency of 5.3-10% from the laser to electrons producing the bremsstrahlung. To test the validity of the inferred electron parameters, modeling of bremsstrahlung data for a 100 μm Cu foil attached on a CH backing is underway. Details of the analysis method and a comparison of inferred electron information for the two target types with and without strong electron recirculation will be presented at the conference.