Verification of unevaluated nonlinear optical process of DAST crystal using the prism coupled Cherenkov phase matching method

The 4-N, N-dimethylamino-4′-N'-methyl stilbazolium tosylate (DAST) crystal has a high figure of merit among nonlinear optical crystals [1]. In second-order nonlinear optical (NLO) processes using a DAST crystal, the $d_{111}$ process generally used is the process of generating a-axis polarized light from incident $a$ -axis polarized light. However, there has been very little investigation of other effective nonlinear processes utilizing other second-order NLO processes. In this study, we investigated generation of terahertz (Thz) waves via the $d_{133}$ process of the DAST crystal using the prism-coupled Cerenkov phase matching (PCC-PM) method [2], [3]. THz waves were generated efficiently using the $d_{133}$ process, and the magnitude of the nonlinear optical coefficient $d_{133}$ estimated from the THz intensity ratio was 34.1 pm/V. These results indicate that PCC-PM can be used to examine unevaluated $d$ -values of NLO crystals and estimate their values.