Interaction of extreme ultraviolet laser radiation with solid surface: ablation, desorption, nanostructuring

摘要

The area, where interaction of focused XUV laser radiation with solid surface takes place, can be divided according to local fluency into desorption region (if fluency is larger than zero and smaller than ablation threshold) and ablation region (if fluency is equal or larger than this threshold). It turned out that a direct nanostructuring (e.g. imprinting diffraction pattern created on edges of windows of proximity standing grid) is possible in the desorption region only. While for femtosecond pulses the particle (atom/molecule) removal-efficiency η in the desorption region is very small (η＜ 10%), and hence, it can be easily distinguished from the ablation region with η ～ 100%, for nanosecond pulses in desorption region this η rises at easily ablated materials from 0% at the periphery up to ～ 90% at the ablation contour and, therefore, the boundary between these two regions can be found with the help of nanostructuring only. This rise of removal efficiency could be explained by gradually increased penetration depth (due to gradually removed material) during laser pulse. This is a warning against blind using crater shape for fluency mapping in the case of long laser pulses. On the other hand it is a motivation to study an ablation plum (or ablation jet) and to create a knowledge bank to be used at future numerical modeling of this process.