Simultaneous second-harmonic generation and femtosecond-pulse compression in aperiodically poled KTiOPO_4 with a RbTiOAsO_4-based optical parametric oscillator

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Abstract
We have obtained both extracavity and intracavity simultaneous second-harmonic generation and compression of signal pulses at 1.25 μm 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.