This paper deals with prediction of extreme ultraviolet (XUV) laser ablation of lithium fluoride at nanosecond timescales. Material properties of lithium fluoride were determined based on bibliographic survey. These data are necessary for theoretical estimation of surface removal rate in relevance to XUV laser desorption/ablation process. Parameters of XUV radiation pulses generated by the Prague capillary-discharge laser (CDL) desktop system were assumed in this context. Prediction of ablation curve and threshold laser fluence for lithium fluoride was performed employing XUV-ABLATOR code. Quasi-random sampling approach was used for evaluating its predictive capabilities in the means of variance and stability of model outputs in expected range of uncertainties. These results were compared to experimental data observed previously.
Availability of numerical model providing reliable estimation of the parameters of ablation processes induced by extreme ultraviolet laser pulses in the range of nanosecond and sub-picosecond timescales is highly desirable for recent experimental research as well as for practical purposes. Performance of the one-dimensional thermodynamic code (XUV-ABLATOR) in predicting the relationship of ablation rate and laser fluence is investigated for three reference materials: (i) silicon, (ii) fused silica and (iii) polymethyl methacrylate. The effect of pulse duration and different material properties on the model predictions is studied in the frame of this contribution for the conditions typical for two compact laser systems operating at 46.9 nm. Software implementation of the XUV-ABLATOR code including graphical user's interface and the set of tools for sensitivity analysis was developed. Global sensitivity analysis using high dimensional model representation in combination with quasi-random sampling was applied in order to identify the most critical input data as well as to explore the uncertainty range of model results.
Single crystals of two fluorides (LiF and CaF2) and a tungstate (PbWO4) were irradiated by nanosecond pulses of 46.9-
nm radiation provided by 10-Hz capillary-discharge Ne-like Ar laser (CDL). The damage threshold was determined in
LiF using the CDL beam focused by a Sc/Si multilayer-coated spherical mirror. Irradiated samples have been
investigated by Nomarski (DIC - Differential Interference Contrast) microscopy and optical (WLI - white light
intereferometry) profiler. After an exposure by a certain number of CDL pulses, an ablation rate can be calculated from
WLI measured depth of the crater created by the XUV ablation. Potential use of XUV ablation of ionic crystals in pulsed
laser deposition (PLD) of thin layers of such a particular material, which is difficult to ablate by conventional UV-Vis-
NIR lasers, is discussed in this contribution.
The desktop capillary-discharge Ne-like Ar laser (CDL) providing 10-μJ nanosecond pulses of coherent 46.9-nm
radiation with a repetition rate up to 12 Hz was developed and built at the Colorado State University in Fort Collins and
then installed in Prague. The beam of the laser was focused by a spherical mirror covered with Si/Sc multilayer coating
onto the surface of poly(methyl methacrylate) - PMMA. Interaction parameters vary by changing the distance between
sample surface and beam focus. The samples were exposed to various numbers of shots. Analysis of damaged PMMA by
atomic force (AFM) and Nomarski (DIC - differential interference contrast) microscopes allows not only to determine
the key characteristics of the focused beam (e.g. Rayleigh's parameter, focal spot diameter, tight focus position, etc.) but
also to investigate mechanisms of the radiation-induced erosion processes.