Using room-temperature parametric oscillation of a LiNbO<sub>3</sub> crystal pumped by a <i>Q</i>-switched Nd:YAG laser with a simple configuration, we have realized a widely tunable coherent terahertz- (THz-) wave source in the range between 1 and 3 THz. Inasmuch as the THz wave is affected by total internal reflection at the crystal edge, we used a Si prism coupler to couple out the THz wave. We introduce an arrayed Si-prism coupler that increases the efficiency and decreases the diffraction angle. By use of the arrayed-prism coupler, there is a sixfold increase in coupling efficiency and a 40% decrease in the far-field beam diameter, compared with the use of a single-prism coupler. We discuss the negative effect of the free carriers at the Si-prism surface that is excited by the scattered pump beam, and the positive effect of cavity rotation on the unidirectional radiation of the THz wave from a Si prism.
© 2001 Optical Society of America
(140.3070) Lasers and laser optics : Infrared and far-infrared lasers
(190.4410) Nonlinear optics : Nonlinear optics, parametric processes
(190.4970) Nonlinear optics : Parametric oscillators and amplifiers
(230.5480) Optical devices : Prisms
Kodo Kawase, Jun-ichi Shikata, Hiroaki Minamide, Kazuhiro Imai, and Hiromasa Ito, "Arrayed silicon prism coupler for a terahertz-wave parametric oscillator," Appl. Opt. 40, 1423-1426 (2001)