X-ray lasers as probes to measure plasma ablation rates

The rate of laser ablation at irradiances of ~2x10 14 Wcm -2 of solid iron and aluminum has been measured using the transmission of a neon-like zinc X-ray laser at 21.2 nm through thin iron and aluminum targets. It is shown that the opacity of ablated material falls rapidly with increasing temperatures and decreasing density from the solid value. As ablated plasma becomes transparent to the X-ray laser flux, the thickness of solid, unablated material and hence the rate of ablation can be measured from time resolved X-ray laser transmission. A self-regulating model of laser ablation and fluid code simulations with absorption to thermal plasma of 5-10% show agreement with our measured ablation rates.