Laser irradiation of disk targets at 0.53 μm wavelength

Abstract

Results and analyses are presented for laser irradiation of Be-, CH-, Ti-, and Au-disk targets with 0.53 μm light in 3–200 J, 600–700 psec pulses, at nominal incident intensities from 3×1013 to 5×1015 W/cm2. The measured absorptions are higher than observed in similar 1.06 μm irradiations, and are largely consistent with modeling which shows the importance of inverse-bremsstrahlung and Brillouin scattering. Observed red-shifted back-reflected light shows that Brillouin scattering occurs at low to moderate levels. Backscattering fractions up to 30% were observed in the f/2 focusing lens. The measured fluxes of multi-keV x rays indicate hot-electron fractions of 1% or less, with temperatures of 6 to 20 keV which are consistent with resonance absorption or perhaps 2ωpe. Measurements show 30%–50% efficient conversion of absorbed light into sub-keV x rays, with time-, angular-, and spatial-emission distributions which are generally consistent with non-local-thermodynamic-equilibrium modeling using inhibited thermal electron transport.