Self-phase-locked degenerate femtosecond optical parametric oscillator.

We demonstrated a stable degenerate synchronously pumped femtosecond optical parametric oscillator (SPOPO) as a divide-by-2 subharmonic generator. The SPOPO exhibited passive all-optical self-phase-locking between the pump and signal/idler and thus required no external electronic feedback to produce the phase-locked subharmonic. We employed a type I phase-matched, 1-mm-long, periodically poled MgO:LiNbO3 crystal as the nonlinear gain element and an 80 MHz mode-locked Ti:sapphire laser with 180 fs pulses tuned at 775 nm as the pump.