Broadband, rapidly tunable Ti:sapphire-pumped BiB₃O₆ femtosecond optical parametric oscillator

We report a femtosecond optical parametric oscillator (OPO) based on the nonlinear material BiB₃O₆ (BIBO) pumped directly by a Kerr lens mode-locked Ti:sapphire laser. Using a 1.5 mm long BIBO crystal cut at θ=11.4° for collinear type I (e→o+o) phase matching in the xz optical plane, femtosecond signal pulses across 1.4-1.6 μm, and idler pulses across 1.6-1.87 μm spectral range are generated, limited by the reflectivity bandwidth of the OPO mirrors. The high nonlinear gain and large spectral acceptance for type I interaction in the xz plane of BIBO permit rapid and continuous tuning across the entire range by simple fine adjustment of OPO cavity delay or through small changes in the pump wavelength, without varying any other parameters. Additionally, owing to the near-zero group velocity mismatch and dispersion, the OPO supports broad spectrum as wide as 33 nm, which results in self-compressed signal pulses. For 150 fs pump pulses, signal pulses with durations down to 106 fs with a time-bandwidth product of 0.48 are obtained without the need for intracavity dispersion compensation.