Nonlinear optical coefficients are important parameters for nonlinear optical crystals. Based on the previously disclosed ${\rm{BaG}}{{\rm{a}}_4}{\rm{S}}{{\rm{e}}_7}$ crystal coefficients, the optimum phase-matching direction with the largest effective nonlinear optical coefficient appears in the second octant (${{90}}^\circ \lt \theta \lt {{180}}^\circ$, ${{0}}^\circ \lt \phi \lt {{90}}^\circ$). In this study, a recalibration was performed using the second-harmonic-generation method, and it was confirmed that the optimum phase-matching direction of the ${\rm{BaG}}{{\rm{a}}_4}{\rm{S}}{{\rm{e}}_7}$ crystal is located in its $XZ$ principal plane ($\phi = {{0}}^\circ$). Therefore, this study will serve as a good reference for future applications of this excellent crystal.

中文翻译：

---

使用二次谐波产生法重新校准 BaGa4Se7 晶体的非线性光学系数

非线性光学系数是非线性光学晶体的重要参数。基于之前公开的${\rm{BaG}}{{\rm{a}}_4}{\rm{S}}{{\rm{e}}_7}$晶体系数，最佳相位匹配方向最大的有效非线性光学系数出现在第二个八分圆 ( ${{90}}^\circ \lt \theta \lt {{180}}^\circ$ , ${{0}}^\circ \lt \ phi \lt {{90}}^\circ$）。在这项研究中，使用二次谐波生成方法进行了重新校准，并确认了${\rm{BaG}}{{\rm{a}}_4}{\ rm{S}}{{\rm{e}}_7}$晶体位于其$XZ$主平面（$\phi = {{0}}^\circ$）。因此，本研究将为这种优良晶体的未来应用提供良好的参考。