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A tabletop femtosecond time-resolved soft x-ray transient absorption spectrometer Rev. Sci. Instrum. 79, 073101 (2008);We show experimentally the possibility of nanostructuring (about 20 nm) of gold surface by picosecond soft x-ray single pulse with low fluence of $20 mJ/cm 2 . The nanometer-scale changes of the surface structure are due to the splash of molten gold under fluence gradient of the laser beam. In addition, the ablation process occurs at slightly higher fluence of $50 mJ/cm 2 . The atomistic model of ablation is developed which reveals that the low threshold fluence of this process is due to the build-up of the high electron pressure and the comparatively low electron-ion energy relaxation rate in gold. The calculated ablation depths as a function of the irradiation fluence are in good agreement with the experimental data measured for gold surface modification with ultra-short duration soft x-ray and visible lasers. V C 2012 American Institute of Physics.

The results of theoretical and experimental studies of ablation of LiF crystal by X-ray beam having photons with 89.3 eV and very short duration of pulse τ = 7 ps are presented. It is found that the crater is formed for fluences above the threshold F abl ≈ 10mJ/cm 2 . Such a small threshold is one order of magnitude less than the one obtained for X-ray ablation by longer (nanoseconds) pulses. The theory explains this dramatic difference as a transition from more energy-consuming evaporative ablation to spallative ablation, when the pulse duration decreases from ns to ps time ranges. Previously, the spallative mechanism of ablation was exclusively attributed to removal of target materials of metal and semiconductor by the short laser pulses with optical photons ∼ 1eV. We demonstrate that tensile stress created in dielectrics by short X-ray pulse can produce spallative ablation of target even for drastically small X-ray fluences.

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We demonstrate high quality, single-shot in situ imaging of the focused Ag x-ray laser (XRL) at 13.9 nm with 700 nm spatial resolution by color center formation in LiF. The flux and intensity for the color center formation in LiF are evaluated from the experimental data. Comparisons with previous reports show that the threshold x-ray flux for the color center formation in LiF for the 13.9 nm, 7 ps Ag XRL is 3 orders of magnitude less than that with the 46.9 nm, 2 ns capillary discharge Ar XRL.