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

Characteristics of fast electrons produced in intense short-pulse laser-solid interaction were experimentally and numerically investigated. The experiment was carried out using a 50 TW Leopard laser (15J, 0.35 ps, 2×10¹⁹ W/cm²) at UNR. The laser-target interaction generates relativistic electrons predominantly by the ponderomotive potential. Subsequently, the electron transport in a target produces bremsstrahlung and escaping electrons that were recorded by two absolutely calibrated filter stack spectrometers and a magnet electron spectrometer, respectively. The angularly resolved bremsstrahlung was then modeled with a 3-D hybrid particle-in-cell code, LSP, by varying divergence angles and electron beam energies, while the slope temperature was estimated from an exponential fit to the measured electron spectrum. The fitting was performed for a 100 μm Cu foil with and without a CH backing. The divergence angle and conversion efficiency from laser to electrons producing bremsstrahlung are found to be ∼55° and ∼7% for the Cu-CH target. While a similar conversion efficiency is obtained for both targets, it is found that the calculated bremsstrahlung at the detector positions is relatively independent of the divergence angle for the Cu target due to strong refluxing.