Ablation dynamics of solids heated by femtosecond laser pulses
P SOC PHOTO-OPT INS 4423 (2001) 186-196
Abstract:
Ultrafast time resolved microscopy of femtosecond laser irradiated surfaces reveals a universal feature of the ablating surface on nanosecond time scale. All investigated materials show rings in the ablation zone, which were identified as an interference pattern (Newton fringes). Optically sharp surfaces occur during expansion of the heated material as a result of anomalous hydrodynamic expansion effects. Experimentally, the rings are observed within a certain fluence range which strongly depends on material parameters. The lower limit of this fluence range is the ablation threshold. We predict a fluence ratio between the upper and the lower fluence limit approximately equal to the ratio of critical temperature to boiling temperature at normal pressure. This estimate is experimentally confirmed on different materials (Si, graphite, Au, Al).Characterization of a broadband multi-keV laser plasma x-ray source for femtosecond time-resolved EXAFS
P SOC PHOTO-OPT INS 4504 (2001) 49-55
Abstract:
Recent advances in femtosecond laser plasma x-rays sources have resulted in several experiments to explore the dynamics of physical and chemical processes on the femtosecond time scale. We present our most recent progresses on the development of an intense broadband x-ray source in the multi-keV range, for application to time-resolved EXAFS experiments. Experiments have been realized with two different CPA laser systems having different pulse durations and characteristics. X-ray emissions in the 5KeV range generated from solid targets with the MRS Nd:Glass laser (400fs, high contrast) and the UCSD Ti:Sapphire laser (20fs, 20Hz) have been characterized through high resolution and time resolved x-ray spectroscopy. The application of this source to time resolved EXAFS measurements with a subpicosecond time resolution will also be discussed.Direct observation of ultrafast non-thermal melting by ultrafast x-ray diffraction
SPRINGER SERIES CHEM 66 (2001) 276-280
Abstract:
Ultrafast nonthermal melting of femtosecond laser-irradiated germanium was observed directly for the first time using sub-picosecond, 1.54-angstrom x-ray diffraction. Such measurements allow the study of transient atomic motion fundamental to many processes in physics, chemistry, and biology.Femtosecond laser-induced ablation of graphite
SPRINGER SERIES CHEM 66 (2001) 425-427
Abstract:
The dynamics of fs-laser ablation of graphite has been investigated experimentally and theoretically. The experimental observation of two different ablation mechanisms is supported by molecular dynamics calculations, which incorporate the changes of the interatomic potentials due to electronic excitation.Femtosecond x-ray measurement of ultrafast melting and large acoustic transients
PHYSICAL REVIEW LETTERS 87:22 (2001) art. no.-225701