Temperature gradients in solid targets irradiated by high intensity short pulse laser*

It has been observed that there exists a rapid decrease in thermal temperature in solid targets, as a function of depth, when irradiated by a high intensity short pulse laser. This phenomenon is further investigated using the Titan short pulse laser with intensities greater than 10$^{20}$ W/cm$^2$ and buried layer targets. The longitudinal temperature profile is determined by measuring K-shell spectra from a 0.4 $\mu$m copper tracer layer placed at various depths (ie. 0-1.5 $\mu$m) within the 2.4 $\mu$m thick target. To study origins of K-shell x-rays in both space and time, a model involving hydrodynamics code HYADES and non-LTE atomic code FLYCHK has been developed. In addition, effect of the fast electron population on K-shell spectra is examined. Preliminary simulation results have produced good agreement with experimental measurements.