Cascaded Terahertz Parametric Generation Under Noncollinear Phase-Matching Condition

We directly observed terahertz (THz) waves generated in a cascading manner under noncollinear phase-matching conditions in a THz parametric generator. Although cascading induced by collinear phase matching has been extensively studied, cascading featuring noncollinear phase matching, using devices such as our injection-seeded THz parametric generator (is-TPG), has received less attention. However, an understanding of is-TPG cascading is required not only for the further development of THz-wave sources but also for THz-range parametric detection and amplification; direct observations are essential. Here, we used a high-power seed beam to induce cascading efficiently; when the crystal was tilted, we detected new higher-order THz waves near the end face. To the best of our knowledge, no previous study has described THz waves generated by cascading under noncollinear phase-matching conditions. We present empirical data that will greatly aid the theoretical exploration of parametric TH-wave generation. Our work paves the way toward enhancement of the output powers of THz sources.