X-ray spectroscopy of laser produced Al plasma near the target surface in a laser ion source

Abstract

The spatially resolved x-ray spectrum of a laser produced Al plasma near the target surface has been obtained in the energy range of 1.5–2.2 keV using a compact flat crystal spectrometer. The widely used temperature and density diagnostics, the line ratios of Lyα/Heβ and IC/Heα, were measured and compared with the calculation results of a steady-state collisional-radiative model so that the temperature and density profiles with a spatial resolution of 55 µm were obtained within 200 µm from the target plane. The plasma parameters derived from the spatially integrated spectrum were used to calculate the ionization state distribution near the target surface with the steady-state model, and the result was compared with the ion charge state distribution measured with an Electrostatic Ion Analyzer (EIA) at a distance of 4.2 m from the target surface. The validity of the steady-state model and the difference between the calculated ion charge state distribution and that measured with the EIA are discussed.