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The recent commissioning of a X-ray free-electron laser triggered an extensive research in the area of X-ray ablation of high-Z, high-density materials. Such compounds should be used to shorten an effective attenuation length for obtaining clean ablation imprints required for the focused beam analysis. Compounds of lead (Z=82) represent the materials of first choice. In this contribution, single-shot ablation thresholds are reported for PbWO4and PbI2exposed to ultra-short pulses of extreme ultraviolet radiation and X-rays at FLASH and LCLS facilities, respectively. Interestingly, the threshold reaches only 0.11 mJ/cm2 at 1.55 nm in lead tungstate although a value of 0.4 J/cm2is expected according to the wavelength dependence of an attenuation length and the threshold value determined in the XUV spectral region, i.e., 79 mJ/cm2at a FEL wavelength of 13.5 nm. Mechanisms of ablation processes are discussed to explain this discrepancy. Lead iodide shows at 1.55 nm significantly lower ablation threshold than tungstate although an attenuation length of the radiation is in both materials quite the same. Lower thermal and radiation stability of PbI2is responsible for this finding.

The irradiation effects of multiple ultrafast shots of laser beams with estimated fluences of some tens of mJ/cm2on a EUV Mo/Si multilayer have been studied. Irradiation damage has been induced by multiple shots of two different lasers (100 fs 400 nm the first, 1.5 ns 46.9 nm the second). The study has been motivated by the need of multilayer Mo/Si optics for the delay lines of the FEL source FERMI@Elettra, where these mirrors will be used to reflect 100 fs pulses at 13 nm with a fluence of some mJ/cm2. The analysis has been performed by means of different techniques as EUV and soft X-ray reflectivity, XPS, and Standing wave enhanced XPS. Simulations have been carried on by means of an indigenously developed software OPAL (Optical Properties of Anisotropic Layers) for the calculation of the absorbed energy by the stratified medium. AFM and SEM surface images have been also acquired. In the irradiation at 400 nm, we observed a significant change in the multilayer performance at fluences of 100 mJ/cm2and above with a significant reduction of reflectivity. Spectroscopic analysis allowed to correlate the decrease of reflectivity with the degradation of the multilayer stacking, ascribed to Mo-Si intermixing at the Mo/Si interfaces of the first few layers, close to the surface of the mirror. Preliminary tests have been also performed on the sample irradiated at 46.9 nm.