Investigation of energy partitioning from Leopard short-pulse laser interactions in mass limited targets

The energy distribution in the interaction of a high-intensity, short-pulse laser with a mass limited target was investigated by simultaneously collecting x-ray and particle data. The Leopard laser system at the Nevada Terawatt Facility delivered 15 J of energy in a 350 fs pulse duration. With a beam spot size limited to within 8$\mu $m, the target interaction achieved a peak intensity of 10$^{19}$ W/cm$^{2}$ at 20$^{\circ}$ incidence. The size of the Cu foil targets was varied from 2 -20 $\mu $m in thickness and from 50 by 50 $\mu $m to 2000 by 2000 $\mu $m in surface area. A Bragg crystal x-ray spectrometer and a spherical crystal imager were used to measure 7.5 -9.5 keV x-rays and 8.05 keV monochromatic x-ray images respectively. The escaping electrons and protons in the rear were monitored with a magnet-based electron spectrometer and radiochromic film. Preliminary results show both a decrease of the K$\beta $/K$\alpha $ ratio\footnote{P. Nilson et al., PRE \textbf{79, }016406 (2009).} and a stronger He$\alpha $ emission for smaller sized targets, less than 250 by 250 $\mu $m. The detailed analyses of the K$\alpha $ images and particle data will be presented.