X-ray laser-induced ablation of lead compounds

Abstract

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 PbWO 4 and PbI 2 exposed to ultra-short pulses of extreme ultraviolet radiation and X-rays at FLASH and LCLS facilities, respectively. Interestingly, the threshold reaches only 0.11 J/cm 2 at 1.55 nm in lead tungstate although a value of 0.4 J/cm 2 is expected according to the wavelength dependence of an attenuation length and the threshold value determined in the XUV spectral region, i.e., 79 mJ/cm 2 at 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 PbI 2 is responsible for this finding.

Fluence thresholds for grazing incidence hard x-ray mirrors

“…In the case of B 4 C at 12 keV, only a lower bound could be given due to the lack of visible damage. We also note that the estimated beam size and shape were consistent with those determined by normal incidence measurements taken on lead(II) iodide 9 and on silicon oxide. 10 It is of note that the fluence damage thresholds are far higher than the values obtained for normal incidence measurements or measurements conducted at lower photon energies.…”

Absolute pulse energy measurements of soft x-rays at the Linac Coherent Light Source

“…Moreover, single-shot ablation thresholds of selected high-Z high-density materials [17], which strongly absorb the LCLS radiation, were determined by means of LCLS pulse energy distributions. Other threshold values [34] obtained during the commissioning validated the Transfer-GMD measurements as well. Figure 6 shows the transmission of the SXR instrument for different photon energies, summarizing the comparison of the FEL average pulse energy measured by the Transfer-GMD and the LCLS gas detectors.…”