Tunable, High-Repetition-Rate, Femtosecond Optical Parametric Oscillator in the Visible

Efficient generation of tunable femtosecond pulses in the visible by internal frequency doubling of an optical parametric oscillator (OPO) based on 1-mm-thick periodically-poled LiNbO₃ (PPLN) is reported. Synchronously pumped by a Kerr-lens-mode-locked Ti:sapphire laser at 76 MHz at 810 nm, infrared femtosecond signal pulses across 1330-1570 nm are generated by the OPO. A 1-mm-thick crystal of BiB₃O₆ (BIBO) is used internal to the OPO cavity to obtain efficient frequency doubling of the signal pulses with up to 260 mW of average power for 1.51 W of input pump power. Because of the high nonlinear gain and phase-matching acceptance in PPLN and BIBO, convenient static tunability is achieved through adjustment the OPO cavity delay without the need to vary any other parameter. Using two pairs of prisms for intracavity dispersion compensation, near-transform-limited pulses with durations down to 140 fs are generated for 185-fs input pump pulses.