A large unexamined second-order nonlinear optical (NLO) process is found in a 4-N,N-dimethylamino-4’-N’-methyl stilbazolium tosylate (DAST) crystal, which has a large figure of merit among NLO crystals. In second-order NLO processes using a DAST crystal, the ${\chi}_{111}^{(2)}$ process of light excitation is commonly used, involving a-axis polarized light excitation with light generation of a-axis polarized light. However, there have been few studies of other second-order NLO susceptibility processes to date. In this Letter, terahertz (THz) wave generation via second-order NLO processes based on the ${\chi}_{133}^{(2)}$ second-order NLO susceptibility of the DAST crystal was investigated. By adjusting the polarization direction of the excitation light using a prism-coupled Cerenkov phase-matching method, efficient generation of THz waves was achieved using a process involving ${\chi}_{133}^{(2)}$. The magnitude of the NLO constant ${\chi}_{133}^{(2)}$ estimated from the THz intensity ratio was 77.8 pm/V. These results indicate that prism-coupled Cherenkov phase matching can be used to identify undiscovered NLO processes for NLO crystals.

中文翻译：

---

二阶非线性光学磁化率的非线性光学过程 $ {\ chi} _ {133} ^ {（2）} $ 在有机非线性光学晶体DAST中

在4-N，N-二甲基氨基-4'-N'-甲基苯乙烯基唑鎓甲苯磺酸盐（DAST）晶体中发现了未经审查的大型二阶非线性光学（NLO）过程，该晶体在NLO晶体中具有很大的品质因数。在使用DAST晶体的二阶NLO过程中，通常使用$ {\ chi} _ {111} ^ {（2）} $光激发过程，包括a轴偏振光激发和a轴产生光偏振光。但是，迄今为止，对其他二阶NLO敏感性过程的研究很少。在这封信中，通过基于$ {\ chi} _ {133} ^ {（2）} $的二阶NLO过程生成太赫兹（THz）波研究了DAST晶体的二阶NLO敏感性。通过使用棱镜耦合切伦科夫相位匹配方法调整激发光的偏振方向，可以使用涉及$ {\ chi} _ {{133} ^ {（2）} $的过程有效地产生THz波。根据太赫兹强度比估算的NLO常数$ {\ chi} _ {133} ^ {（2）} $的大小为77.8 pm / V。这些结果表明，棱镜耦合的契伦科夫相位匹配可用于识别未发现的NLO晶体NLO过程。