Second-order nonlinear optical materials for efficient generation and amplification of temporally-coherent and narrow-linewidth terahertz waves

We have considered forward and backward optical parametric oscillation and amplification, and difference-frequency generation for efficiently generati ng and amplifying terahertz waves in several second-order nonlinear optical materials. We have used a single crystal of CdSe as an example. We have al so investigated GaSe, periodically-poled LiNbO3 and LiTaO3, and diffusion-b onded-stacked GaAs and GaP plates. The advantage of using birefringence in CdSe and GaSe is tunability of the output terahertz frequency. Furthermore, both CdSe and GaSe can be used to achieve the backward parametric oscillat ion without any cavity. On the other hand, in periodically-poled LiNbO3 and LiTaO3, one can take advantage of large diagonal elements of second-order nonlinear susceptibility tensor. In the diffusion-bonded-stacked GaAs and G aP plates, quasi-phase matching can be achieved by alternatively rotating t he plates. We have shown that it is feasible to achieve forward optical par ametric oscillation in the THz domain using these plates. The advantage of using coherent parametric processes is possibility of efficiently generatin g and amplifying temporally-coherent and narrow-linewidth terahertz waves. Compared with a noncollinear configuration, by using the parallel wave prop agation configurations, the conversion efficiency can be higher because of longer effective interaction length among all the waves.