Observation and modeling ablation threshold features of dielectrics irradiated by ultrashort pulses of soft X-ray transient collisional and free electron lasers

Inogamov, N. A.*; Faenov, A. Y.; Pikuz, T.*; Zhakhovski, V.*; Skobelev, I.*; Khokhlov, V.*; Anisimov, S. I.*; Fortov, V. E.*; Fukuda, Yuji; Kato, Yoshiaki* ; Tanaka, Momoko; Kishimoto, Maki; Ishino, Masahiko; Nishikino, Masaharu; Bulanov, S. V.; Kawachi, Tetsuya; Nagasono, Mitsuru*; Ohashi, Haruhiko*; Yabashi, Makina*; Tono, Kensuke*; Semba, Yasunori*; Togashi, Tadashi*; Ishikawa, Tetsuya*

The results of theoretical and experimental studies of ablation of LiF crystal by X-ray laser and FEL beams having photons with 89.3 eV and 20 eV with very short duration of pulse 7 ps and 300 fs are presented. It is found that the crater is formed for fluencies above the threshold Fabl about 10 mJ/cm: 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 change-over from more energy consuming evaporative ablation to spallative ablation, when the pulse duration decreases from ns to ps time ranges. 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 fluencies, which open new opportunities for material nano processing.