Investigation of fast electron properties from hybrid-PIC modeling of angularly resolved bremsstrahlung*

Characterization of fast electrons generated by ultra-intense short-pulse lasers is important for many high-energy x-ray applications such as broadband Compton radiography and K-a radiography. An experiment was conducted to study the electron energy spectrum, divergence, and conversion efficiency of fast electrons by irradiating a 100 µm thick Cu foil with the 50 TW Leopard laser at the Nevada Terawatt Facility. Bremsstrahlung and escaped electrons were recorded with differential filter stack spectrometers at 22° and 40° from the laser axis and a magnetic electron spectrometer along the laser axis. From measurements with the electron spectrometer, a slope temperature of 1.1 MeV was inferred. Using the inferred electron spectrum in a hybrid particle-in-cell code, LSP, with a 2D Cartesian coordinate, we fit the bremsstrahlung signals at the two angles simultaneously by varying the divergence angle and energy of fast electrons injected. A best fit of the data was found for the conversion efficiency of ~ 6% and a divergence angle of ~10°. Details of this experimental and numerical study will be presented.