Spallative Ablation of Metals and Dielectrics

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 tau = 7 ps are presented. It is found that the crater is formed for fluences above the threshold F-abl approximate to 10 mj/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 similar to 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. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim