Self-phase modulation of mid-infrared femtosecond pulses in semiconductor materials

Abstract

Coherent spectral expansion of the mid-infrared femtosecond pulses is beneficial for monitoring and controlling molecular vibrational dynamics. We investigate the spectral broadening of mid-infrared pulses due to nonlinear optical effects in semiconductor materials. The mid-infrared pulses of 100 fs duration and 180 cm^-1 bandwidth at the center wavelength of about 5 micron are focused onto the semiconductor materials. With only few-micro-joule pulse energy, the spectral broadening by a factor of more than 3 is observed for Si, Ge, and GaAs. The output spectral component extends from 1500 cm^-1 to 3000 cm^-1. The intensity and the phase profiles of the self-phase modulated pulses are characterized by the modified auto-interferometric autocorrelation method and its phase-retrieval algorithm, indicating the spectral phase to be compensated for pulse compression.