Modification of semiconductor surfaces irradiated by single intense fs-laser pulses

Summary form only given. Material modification by ultrashort laser pulses represents a promising tool for a variety of technological applications. Nevertheless the mechanisms of femtosecond laser ablation are still not well understood. A striking feature of femtosecond laser ablation is the extremely sharp threshold; i.e. an increase of the laser fluence by less than one percent leads to the removal of a macroscopic amount of the material. Trying to understand the physical nature of this process we have conducted a detailed investigation of the final ablation morphology produced on GaAs[100] and Si[100] surfaces by single intense fs-laser pulses using optical interference, differential interference contrast (DIC), atomic force (AFM) and scanning electron (SEM) microscopies. Our craters are different from those produced under very tight focusing conditions (6 /spl times/ 6 /spl mu/m FWHM). We have also observed similar change in the crater shape when focusing very tightly. The influence of the focusing conditions on the mechanisms of final crater formation is the subject of further investigations.