Abstract-Efficient tunable terahertz generation via noncollinear phase matching in the ZnGeP2 crystal

 

Fangjie Li, Kai Zhong, Hongzhan Qiao, Kefei Liu, Xianzhong Zhang, Degang Xu,  Jianquan Yao, 

https://www.osapublishing.org/josab/abstract.cfm?uri=josab-37-12-3857

A novel noncollinear phase-matching (PM) scheme was proposed by introducing a small tunable angle between two pump beams to maximize the effective nonlinear coefficient (𝑑eff$d_{\mathrm{e}\mathrm{f}\mathrm{f}}$) in tunable terahertz wave difference frequency generation in the ZnGeP2${\mathrm{Z}\mathrm{n}\mathrm{G}\mathrm{e}\mathrm{P}}_2$ crystal. Compared with the collinear PM condition, the noncollinear geometry transfers the PM angle to be around 𝜃=90∘$\theta ={90}^{\circ }$ for type-II (o−e→o$\mathrm{o}-\mathrm{e}\to \mathrm{o}$) PM to fully use the maximum nonlinear coefficient 𝑑36$d_{36}$, leading to a high conversion efficiency improved by tens of times in theory. Based on the theory of noncollinear PM, the angle-tuning characteristics were calculated and the crystal design was provided for efficient outcoupling. A rigorous theoretical model was built under small-signal approximation to show the affecting factors of noncollinear PM and reveal its superiority compared with collinear PM.

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