Design and angular robustness test of chirped periodically poled lithium niobate crystal for 1064 nm second-harmonic generation experiment
Authors: Liu Li-Qiang , Su Wei-Lun , Liu Jun-Ming , Zou Yu , Hong Li-Hong , Li Zhi-Yuan ,   School of Physics and Optoelectronics, South China University of Technology, Guangzhou 510641, China,   Guangdong Jingchuang Optical Machinery Co., LTD, Guangzhou 510510, China,   State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China
Published: August 2024

A 532-nm solid-state laser, generated by second-harmonic generation (SHG) technology, has become one of the most extensively used lasers in various applications today. In the traditional scheme, the most prevalent SHG crystal of the 532-nm solid-state is lithium borate (LBO), and continues to exhibit insufficient angular robustness and SHG efficiency. In order to overcome these limitations and obtain SHG crystals with better angular robustness, this study starts with a comprehensive theoretical analysis of angular robustness. On this basis, the structure of a chirped periodically poled lithium niobate (CPPLN) crystal is designed by taking into account the desired properties for improving its performance, and then the theoretical simulations and experimental tests are implemented to validate the effectiveness of the designed crystal. The simulation results corroborate the superior angular robustness of the CPPLN crystal. In a range from <inline-formula><tex-math id="M4">\begin{document}$ - {3^ \circ } $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20240778_M4.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20240778_M4.png"/></alternatives></inline-formula> to <inline-formula><tex-math id="M5">\begin{document}$ + {3^ \circ } $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20240778_M5.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20240778_M5.png"/></alternatives></inline-formula>, the designed CPPLN crystal exhibits a maximum SHG efficiency of 0.80% and a minimum one of 0.51%, which indicates that the SHG efficiency of this crystal in this range can be maintained at 60% of the maximum efficiency. The experimental results show that the SHG efficiency can be more than 11 times that of LBO crystal. Moreover, the study indicates that the half width of the actual SHG efficiency near the incident angle of the designed CPPLN crystal can exceed <inline-formula><tex-math id="M6">\begin{document}$ {6^ \circ } $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20240778_M6.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20240778_M6.png"/></alternatives></inline-formula>, demonstrating its excellent tolerance for changes in incident angle. Furthermore, the output spot of the SHG light generated by the designed CPPLN crystal exhibits a standard Gaussian profile, which remains virtually unaffected by the incident angle. In summary, the findings of this research highlight the CPPLN crystal as a promising alternative to LBO, with markedly higher SHG efficiency and better angular robustness. These superior characteristics make the CPPLN crystal a highly attractive candidate for a wide range of laser applications.