Analysis of the simultaneous measurements of iron K- and L-shell radiation from ultrashort laser produced plasmas

Abstract

High resolution x-ray spectra of plasmas produced by the interaction of Ti:Sa laser pulses (duration from 60 fs to 1 ps, and energy from 15 to 128 mJ) with a solid iron target are investigated. Interestingly, both L-shell and K-shell Fe spectra were simultaneously measured using a focusing spectrometer with spatial resolution. In particular, the L-shell Fe radiation from F-, Ne-, and Na-like ions between ∼14–16.3 Å were observed from the first-order reflection with a mica crystal. Simultaneously measured alongside the L-shell radiation was the Fe cold Kα lines (∼1.94 Å), from eighth-order reflection. Two non-LTE Fe kinetic models have been developed to account for the L-shell radiation from the Fe ions and for the K-shell radiation from low ionization stages emitting the Fe cold Kα lines. Preliminary analysis of the simultaneously measured Fe L- and K-shell radiations from changing the time-duration, laser contrast, and focus of the experiments shows varying relative line intensities from different ionization stages. Resulting plasma parameters and their dependence on changing the time-duration, laser contrast, and laser focus will be discussed.