Desorption/ablation of lithium fluoride induced by extreme ultraviolet laser radiation

Abstract

Abstract. The availability of reliable modeling tools and input data required for the prediction of surface removal rate from the lithium fl uoride targets irradiated by the intense photon beams is essential for many practical aspects. This study is motivated by the practical implementation of soft X-ray (SXR) or extreme ultraviolet (XUV) lasers for the pulsed ablation and thin fi lm deposition. Specifi cally, it is focused on quantitative description of XUV laser-induced desorption/ablation from lithium fl uoride, which is a reference large band-gap dielectric material with ionic crystalline structure. Computational framework was proposed and employed here for the reconstruction of plume expansion dynamics induced by the irradiation of lithium fl uoride targets. The morphology of experimentally observed desorption/ablation craters were reproduced using idealized representation (two-zone approximation) of the laser fl uence profi le. The calculation of desorption/ablation rate was performed using one-dimensional thermomechanic model (XUV-ABLATOR code) taking into account laser heating and surface evaporation of the lithium fl uoride target occurring on a nanosecond timescale. This step was followed by the application of two-dimensional hydrodynamic solver for description of laser-produced plasma plume expansion dynamics. The calculated plume lengths determined by numerical simulations were compared with a simple adiabatic expansion (blast-wave) model.

Ablation of single-crystalline cesium iodide by extreme ultraviolet capillary-discharge laser

“…4) decreases, reaching a plateau at 100 pulses. This decrease was previously found for other ionic crystals [15]. This effect could be caused by (a) radiation--induced hardening of the irradiated material and/ or (b) the development of the crater shape, which obstructs the exit of the material from the crater, enhancing its redeposition on the crater wall.…”

“…An analysis of the craters produced at various fl uences enabled determination of the ablation threshold. The experimentally determined value was compared to the value calculated using the XUV-ABLATOR computer code [15].…”

“…This estimation is the upper level of the ablation threshold for a single-shot process because of the declining etch rate. Numerical modelling of the XUV-induced CsI removal, performed with the 1D fi nite-difference Lagrangian code (XUV-ABLATOR [15]), provides a prediction of the maximum CsI etch rate, d 62 ± 11 nm per pulse, at a peak fl uence of 0.375 J/cm 2 achieved in a tight focus. Computer simulations revealing the etch rate dependence on the fl uence ( Fig.…”