Abstract
Absolute X-ray spectroscopic measurements of the lines and continua from space-resolved C6+, C5+, C4+, C3+ ions at the surface of a plane polyethylene target, irradiated by a 1.06 mu m neodymium laser, are interpreted in terms of a collisional-radiative model in which some of the allowed lines are optically thick. The degree of ionization increases monotonically with laser power density over the range 1011 to 2*1012 W cm-2 and the electron energy distributions are strictly Maxwellian. The ion population ratios indicate that the ionization time is of the order of 1 to 10 picoseconds and is limited by thermal expansion within a thin layer whose mean density is approximately 3*1021 cm-3.