Ultrafast phase transitions after femtosecond laser irradiation of indium phosphide

The structural transformation dynamics of single-crystalline indium phosphide irradiated with 150fs laser pulses at 800nm has been investigated by means of time-resolved reflectivity measurements covering a time window from 150fs up to 500ns. The results obtained show that for fluences above the threshold of 0.16J∕cm2 thermal melting of the material occurs on the time scale of 1–2ps, while ablation at higher fluences (>0.23J∕cm2) is preceeded by an ultrafast phase transition (“nonthermal melting”) occurring within 400fs after the arrival of the pulse to the surface. The evolution of the reflectivity on a longer time scale shows a resolidification time typically around 25ns after which an amorphous layer several tens of nanometer thick is formed on the surface.