Pulse-compression mechanism in a synchronously pumped optical parametric oscillator

We describe a mechanism for pulse compression in a length-detuned synchronously pumped optical parametric oscillator. Our model shows that the compression is due to group-velocity walk-off combined with parametric gain depletion. We find excellent agreement between the results of our model and the experimentally observed behavior of our synchronously pumped optical parametric oscillator, including the prediction and the observation of as much as 20-fold compression. Using our model as a basis, we describe the possibilities and the limitations of this technique for generating broadly tunable femtosecond pulses.