Ultrafast phase transitions after femtosecond laser irradiation of indium phosphide.

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