We report a synchronously pumped optical parametric oscillator that generates the sum frequency of the pump and the signal wavelengths. A single KTiOPO<sub>4</sub> (KTP) crystal is used for both parametric generation and sum-frequency generation 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 output beam at 487 nm with 43% power-conversion efficiency. The polarization geometry of simultaneous phase matching requires rotation of the pump polarization before the cavity. Adjusting the group delay between the two orthogonally polarized pump components to compensate for the group-velocity mismatch in the KTP crystal increases the photon-conversion efficiency more than threefold. Angle tuning in conjunction with pump wavelength tuning provides output tunability in the 484–512-nm range. A plane-wave model that takes group-velocity mismatch into account is in good agreement with our experimental results.
© 1999 Optical Society of America
(190.2620) Nonlinear optics : Harmonic generation and mixing
(190.4410) Nonlinear optics : Nonlinear optics, parametric processes
(190.4970) Nonlinear optics : Parametric oscillators and amplifiers
(190.7110) Nonlinear optics : Ultrafast nonlinear optics
(190.7220) Nonlinear optics : Upconversion
Kahraman G. Köprülü, Tolga Kartaloğlu, Yamaç Dikmelik, and Orhan Aytür, "Single-crystal sum-frequency-generating optical parametric oscillator," J. Opt. Soc. Am. B 16, 1546-1552 (1999)