Intensity Correlation Analysis on Blue-Violet Femtosecond Pulses from a Dispersion-Compensated GaInN Mode-Locked Semiconductor Laser Diode

We investigated the spectral and temporal characteristics of blue-violet femtosecond optical pulses generated by a passively mode-locked GaInN laser diode in a dispersion-compensated external cavity. The output optical pulses at 400 nm were analyzed in detail by intensity autoand cross-correlation measurements using second harmonic generation on the surface of a β-BaB2O4 crystal. The obtained results clarified wavelength-dependent chirp characteristics of the optical pulses. The analysis suggested that a large frequency shift due to saturation in the saturable absorber and gain sections played an important role in the generation of femtosecond optical pulses.