Correlation measurements of the phase modulation of radiation with intracavity frequency-doubling of ultrashort pulses

Two techniques are used to obtain quantitative information on the nonlinear phase modulation of ultrashort-pulse (USP) laser radiation in the case of intracavity second harmonic generation (ICSHG). These techniques are: (1) the oscillographic recording of pulse duration and shape and (2) measurements of the USP autocorrelation and cross-correlation functions in the presence and in the absence of ICSHG in an actively mode-locked YAG:Nd(3+) laser, determining train-averaged pulse coherence times and the times of the mutual coherence of neighboring pulses in a train. The results indicate that the model of Apanasevich et al. (1984) adequately describes ICSHG in actively mode-locked lasers, and that the proposed experimental method makes possible the adequate assessment of the phase-modulation scale of the laser radiation.