Posted February 21, 2019 at 11:32 am by xzbbvfvbh

New progress in deep ultraviolet nonlinear optical crystals in China

It has been found that deep-UV VUV, UV and IR grade CaF2 optics with excellent performance have always been a hot spot in the field of functional materials research. Lithium triborate (LBO) crystal is an excellent UV-inorganic nonlinear optical crystal discovered by Fujian structure. It has the advantages of large crystal size, good customized large size and special shape CaF2 optics, wide light transmission range, large multiplication factor and high damage threshold. The best frequency doubling crystal material currently used in high power solid state laser devices. However, due to the small birefringence of the LBO crystal, it is difficult to directly generate a deep ultraviolet coherent light source by phase matching technique. Despite tremendous efforts, it has been found to be difficult to achieve a UV nonlinear optical material that exceeds the LBO crystal. In recent years, scientists have been actively exploring ways to improve LBO crystals to improve their performance.

Under the auspices of the National Natural Science Foundation of China, Wu Kejun, the State Key Laboratory of Structural Chemistry of Fujian Institute of Physical Structures, used computational materials technology to make new progress in broadening the matching range of procurement high efficiency optical window. Based on the first-principles calculation simulation, a method of widening the phase matching range of the nonlinear optical crystal by applying external stress to modulate the birefringence of the nonlinear optical crystal material is proposed. Recent calculations have found that applying tensile stress along the c-axis of the LBO crystal increases optical anisotropy and effectively increases the birefringence of the material. Applying a small external stress (~0.42 GPa) increases the calculated birefringence of the LBO crystal to 0.075, enabling phase matching in a shorter wavelength range. The study also found that the application of external stress can maintain the excellent linear and nonlinear optical properties of the LBO crystal while increasing the birefringence. The research results show that the LBO crystal can realize the “on/off” regulation of the direct multi-frequency output ultraviolet laser through “applying/non-applying” external stress, which provides an important idea for designing new high-power laser switching devices. The related research result “An effective strategy to achieve deeper coherent light for LiB3O5” has been published online in the famous material engineering journal “Material Chemistry” (J. Mater. Chem. C2016, DOI: 10.1039/C5TC03814F). In recent years, research on the performance of functional materials using high-voltage technology has developed rapidly. This computational research work provides important innovative ideas for the performance improvement and regulation of nonlinear optical materials.

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