High-harmonic-repetition-rate, 1 GHz femtosecond optical parametric oscillator pumped by a 76 MHz Ti:sapphire laser.

We demonstrate the generation of femtosecond pulses in a synchronously pumped optical parametric oscillator (SPOPO) at the harmonics of pump repetition rate using a SPOPO cavity longer than the fundamental synchronous length. The SPOPO is based on a 1 mm crystal of periodically poled LiNbO(3) and pumped by a Kerr-lens mode-locked Ti:sapphire laser at 76 MHz. By increasing the SPOPO synchronous cavity length we have generated output signal pulses at successive harmonics of the pump repetition rate up to the 13th harmonic at 988 MHz, where average signal powers of 30 mW are still available for 1.45 W of pump power. The generated signal pulses at 988 MHz are near transform limited with average durations of 227 fs and a time-bandwidth product of 0.41 for 185 fs input pump pulses.