FREQUENCY-SHIFTS IN INJECTION-SEEDED OPTICAL PARAMETRIC OSCILLATORS WITH PHASE MISMATCH

We have observed a frequency shift in the output signal pulses relativ e to the seed frequency in an injection-seeded, singly resonant, criti cally phase-matched, pulsed optical parametric oscillator in which pha se mismatch was intentionally introduced. The observed shifts can be l arge compared with the linewidth of the signal pulse, are approximatel y linear in phase mismatch, and increase with increasing pump fluence. We observe frequency shifts of as much as +/-400 MHz for our 532-nm-p umped, potassium titanyl phosphate ring optical. parametric oscillator . For zero phase mismatch, we observe nearly transform-limited linewid ths of less than 130 MHz. We compare the experimental data to a simple analytic model that overestimates the shifts because it ignores pump depletion. We also compare our measurements with a numerical model tha t calculates the two-dimensional, transient electric fields and the re sultant spectral distributions while explicitly including walk-off, di ffraction, and pump depletion. We find good agreement between the expe rimental data and the results of this model.