In recent years widely tunable terahertz- (THz-) wave generation from LiNbO<sub>3</sub> optical parametric oscillators (OPO’s) has been successfully demonstrated by use of the prism output-coupler method. However, there remains a problem of large absorption loss for generated terahertz waves inside the crystal, so we investigated the cryogenic characteristics of the OPO. We achieved 125-times-higher THz-wave output and 32% reduction of the generation threshold by cooling the crystal to 78 K. This scheme also provides direct loss measurement at THz frequency, and we found that the THz-wave enhancement mechanism is improvement of the gain as well as the reduction of the absorption coefficient.
© 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
(190.5890) Nonlinear optics : Scattering, stimulated
(300.1030) Spectroscopy : Absorption
Jun-ichi Shikata, Manabu Sato, Tetsuo Taniuchi, Hiromasa Ito, and Kodo Kawase, "Enhancement of terahertz-wave output from LiNbO3 optical parametric oscillators by cryogenic cooling," Opt. Lett. 24, 202-204 (1999)