Abstract
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 (${d_{\rm{eff}}}$) in tunable terahertz wave difference frequency generation in the ${{\rm ZnGeP}_2}$ crystal. Compared with the collinear PM condition, the noncollinear geometry transfers the PM angle to be around $\theta = {90}^\circ$ for type-II (${\rm o} - {\rm e} \to {\rm o}$) PM to fully use the maximum nonlinear coefficient ${d_{36}}$, 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.
© 2020 Optical Society of America
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