Soft x-ray spectra of cerium laser-produced plasmas

Abstract

Spectra of laser-produced plasmas of cerium have been recorded in the 1.5 to 15.5 nm spectral region. The plasmas were formed using the frequency doubled pulsed output of a neodymium-doped yttrium aluminium garnet (Nd:YAG) laser at 532 nm. At the power densities incident on-target, ranging from 8.6 × 109-2.1 × 1013 W cm-2, Ce4+ to Ce27+ ions gave rise to emission from Δn = 0, 1 transitions to final states where n = 4. The spectra are dominated by an intense unresolved transition array (UTA) in the 8-10 nm region arising from n = 4 to n = 4 transitions. Two distinct components of this UTA are observed whose appearance is strongly dependent on laser power density, corresponding to transitions involving ions with open 4d and open 4f subshells, the latter at longer wavelengths. Multiple other transition arrays are identified and UTA statistics are given. The analysis was aided by atomic structure calculations and the use of a steady state collisional-radiative model.