Bulk phase explosion and surface boiling during short pulse laser ablation of semiconductors

Summary form only given. Femtosecond laser ablation of semiconductors has been studied in our group with a number of techniques, including time resolved microscopy and time-of-flight mass spectroscopy. The physical pathway which results in the removal of material can be summarised as follows. The laser pulse excites a very dense electron-hole plasma in the semiconductor, leading to nonthermal melting on a sub-picosecond timescale. The liquid is left in a state of high temperature (T>3000 K/sup 2/) and high pressure. The pressure drives expansion of the material into vacuum and homogeneous nucleation of the gas phase (phase explosion) takes place within a few tens of picoseconds. The material decomposes into a non-homogeneous mixture of liquid and gas, eventually transforming into a gas upon further dilution.