Single-crystal sum-frequency-generating optical parametric oscillator

We report a synchronously pumped optical parametric oscillator that generat es the sum frequency of the pump and the signal wavelengths. A single KTiOP O4 (KTP) crystal is used for both parametric generation and sum-frequency g eneration in which these two processes are simultaneously phase matched for the same direction of propagation. The parametric oscillator, pumped by a femtosecond Ti:sapphire laser at a wavelength of 827 nm, generates a blue o utput beam at 487 nm with 43% power-conversion efficiency. The polarization geometry of simultaneous phase matching requires rotation of the pump pola rization before the cavity. Adjusting the group delay between the two ortho gonally polarized pump components to compensate for the group-velocity mism atch in the KTP crystal increases the photon-conversion efficiency more tha n threefold. Angle tuning in conjunction with pump wavelength tuning provid es output: tunability in the 484-512-nm range. A planewave model that takes group-velocity mismatch into account is in good agreement with our experim ental results. (C) 1999 Optical Society of America [S0740-3224(99)01309-0].