Analytic expressions for ultrashort pulse generation in mode-locked optical parametric oscillators

We obtain simple analytic solutions for ultrashort pulse generation in a degenerate mode-locked optical parametric oscillator pumped synchronously by a mode-locked laser. Very short pulses (∼1 psec) are predicted at steady state very close to threshold where pump depletion is negligible; but the parametric pulses broaden to the same order as the pumping laser pulses as soon as pump pulse depletion becomes significant. In the transient buildup regime, where pump depletion is again negligible, pulse widths approximately a quarter of the pump pulse width are obtained.