Simultaneous second-harmonic generation and femtosecond-pulse compression in aperiodically-poled KTiOPO4 with a RbTiOAsO4 -based optical parametric oscillator

We have obtained both extracavity and intracavity simultaneous second-harmonic generation and compression of signal pulses at 1.25 mu m from a synchronously pumped RbTiOAsO4-based optical parametric oscillator with an aperiodically poled crystal of KTiOPO4. The 290-fs input pulses yield temporally compressed frequency-doubled pulses with durations of 120 fs and average output powers of as much as 120 mW. Experimental results are compared with a numerical model in which the temporal and spectral pulse shape and phase of the second-harmonic pulses are calculated with data obtained by characterization of the input pulses by use of the frequency-resolved optical gating technique. We also used the model to optimize the crystal parameters that would result in higher conversion efficiencies and that would enhance pulse compression. (C) 1999 Optical Society of America [S0740-3224(99)00109-5].