Splash-melting nano-meter size modification of metal surfaces induced by soft X-ray laser single pulse

Ishino, Masahiko; Faenov, A. Ya.*; Tanaka, Momoko; Pikuz, T.; Tamotsu, Satoshi*; Hasegawa, Noboru; Nishikino, Masaharu; Starikov, S. V.*; Stegailov, V. V.*; Norman, G. E.*; Fortov, V. E.*; Skobelev, I.*; Kaihori, Takeshi*; Kawachi, Tetsuya

Laser ablation has many technological applications in material micro-meter size processing and fabrication of nano-structures. We show experimentally the possibility of the precise nano-meter size surface structuring of metal aluminum (Al) and gold (Au) surfaces induced by ultra low fluencies of pico-second soft X-ray laser (SXRL) single pulse. The spatially coherent SXRL beam was generated from the silver (Ag) plasma mediums using oscillator-amplifier configuration with Ag double targets. The generated SXRL pulse had the wavelength of 13.9 nm and the duration of 7 ps. On Al surface, the formations of conical structures were observed in the shallow features. On Au surface, the ripple-like structures were observed. The atomistic model of surface modifications is developed that reveals the ultra-low threshold fluency values of this process and suggests it as a splash-melting regime. Our results will open new opportunities for nano-meter size processing for metal surfaces.