Study of energy partitioning in mass limited targets using the 50 TW Leopard short-pulse laser

Mass limited Cu targets were used to study the energy distribution in the interaction of an ultra-intense, short-pulse laser by measuring characteristic x-rays and energetic particles. At the Nevada Terawatt Facility, Leopard delivered 15 J to an 8 $\mu $m spot size in a 350 fs pulse, achieving a peak intensity of 10$^{19}$ W/cm$^{2}$ at 20$^{\circ}$ incidence. The 2 $\mu $m thick Cu foil targets varied in size from 1 mm$^{2}$ to 75 $\mu $m by 60 $\mu $m. A spherical crystal imager and a Bragg crystal x-ray spectrometer were used to measure 8.05 keV monochromatic x-ray images and 7.5-9.5 keV x-rays respectively. A magnet-based electron spectrometer in the rear monitored escaping electrons. Results show a decrease in the absolute yield of both escaped electrons and Cu K-shell x-rays as targets sizes are reduced, while He$\alpha $ emission remains nearly constant. In the smallest target, a bulk temperature of about 150 eV was inferred from the ratio of K$\beta $ to K$\alpha $. The interaction of the Leopard laser with the targets was simulated with 2-D implicit Particle-in-cell code PICLS. Comparisons of the simulation and experiment will be presented.