Laser wavelength dependences of amorphization and crystalization of Si by femtosecond laser pulses

In addition to the non-thermal ablation and the LIPSS (laser induced periodic surface structures) formation, it had been reported that femtosecond laser irradiation induced amorphization of crystalline semiconductor and crystallization of amorphous Si. This paper reports on the laser wavelength dependences of the phase transition of Si by femtosecond laser pulses. Results show that the thickness of amorphized layer does not depend on the number of irradiated laser pulses, but on the laser wavelength. The amorphous layer becomes thinner as the wavelength becomes shorter. The reasons behind these observations are related to the effective light penetration depth of the femtosecond pulses. Decreasing the laser wavelength decreases the amorphization threshold and the crystallization threshold as well.