Analysis of Opaque X-ray Lineshapes from Hot Dense Plasma *

Irradiating solid targets with high intensity lasers creates some of the densest and brightest laboratory plasmas which are often used as a source of relativistic particles and x-rays. This analysis examines a collection of x-ray spectra from the ALEPH 400 nm laser facility at Colorado State University, obtained with a high-resolution Bragg crystal spectrometer. The laser deposited 8-10 J in 45 fs pulses, with an intensity of ∽3x10 22 W/cm², focused onto multilayer targets composed of Al and Ti of varying thicknesses. Titanium plasma becomes highly ionized under these conditions, emitting photons through the resonance transition 1s2p → 1s2 that are energetic enough to escape the dense plasma, but which are susceptible to opacity effects. Resonance line widths were measured and fit to modeled lineshapes in order to gauge the presence and degree of self-reversal, which varies with optical depth and thus Ti layer thickness. Measuring opacity effects for different target parameters can constrain plasma conditions and aid in the understanding of radiation transport within these high temperature, solid-density plasmas.