Recalescence after solidification in Ge films melted by picosecond laser pulses

Thin amorphous Ge films on glass substrates are irradiated by single picosecond (ps) laser pulses and the induced melting and solidification process is followed by means of real-time reflectivity measurements with ps resolution using a setup based on a streak camera. Due to the excellent time resolution achieved in single exposure, the recalescence process occurring upon solidification can be completely resolved by means of an all-optical technique. The results are consistent with the bulk nucleation of the amorphous phase in the supercooled liquid at an extremely large nucleation rate. The massive release of solidification heat causes the reheating and partial remelting of the film after its complete solidification. The occurrence of recalescence after solidification is responsible for the formation of the crystalline phase finally obtained.