X-ray spectroscopy of buried layer foils irradiated at laser intensities in excess of 1020 W/cm2

Abstract

Observations of a rapid decrease in thermal temperature as a function of depth of solid targets irradiated with a short pulse, ultrahigh-intensity laser are reported. This phenomenon is investigated using the Titan short pulse laser with intensities greater than ${10}^{20}\text{W}/{\text{cm}}^2$ interacting with buried layer targets. The longitudinal temperature profile is determined by measuring $K$ -shell spectra from a $0.4\mu \text{m}$ copper tracer layer placed at various depths (i.e., $0–1.5\mu \text{m}$ ) within the $2.4\mu \text{m}$ thick target. It is observed that the line ratios (He-like $K$ -shell lines) as a function of temperature require a consideration of at least three parameters to analyze the $K$ -shell spectra: hot electron population, time-dependent plasma conditions, and opacity. Here, the study of the effect of these three parameters on measured spectra in the short pulse high intensity laser-matter interactions using the atomic model FLYCHK [H.-K. Chung et al., High Energy Density Phys. 1, 3 (2005)] is presented.