Mid- and far-infrared nonlinear optical (NLO) crystal materials have important applications in the fields of lidar, laser communication, infrared telemetry, and photoelectric countermeasures. Phase matching is a key condition for the practical application of NLO materials. At present, the main purpose of adjusting the birefringence of crystals is to compensate for the difference between the refractive index of the fundamental frequency light and the frequency doubled light, thereby achieving the phase matching of NLO crystal materials.
With the support of the strategic leading science and technology project of the Chinese Academy of Sciences and the National Natural Science Foundation of China, Guo Guocong, a researcher at the State Key Laboratory of Structural Chemistry at the Institute of Material Structures of the Chinese Academy of Sciences, adopted the strategy of widening the band gap to adjust the dispersion to achieve the phase of infrared NLO crystal materials match. Through the high-temperature solid-phase method, this study successfully prepared a wide-bandgap (3.93-3.95 eV) molten salt sulfide [ABa3Cl2][Ga5S10] (A= K, Rb, Cs). First-principles calculations have found that the widening of the band gap makes the dispersion curve of the sulfide more gentle in the infrared band compared to its heterogeneous selenide, which in turn shifts the phase-matched cut-off wavelength from 5.7 um blue to 1.7 um, The realization of its phase matching at the traditional fundamental frequency laser (2.0 um) provides a new design idea for obtaining a new phase-matching infrared NLO crystal material.
In addition, the study obtained single crystals of millimeter size. Tests show that these sulfides have the highest laser damage threshold (188-200 MW/cm2 @1064 nm, pulse width 10 ns) and a wide infrared transmission range under the conditions comparable to the NLO coefficient of commercial AgGaS2. 0.35-12.5 um), is an excellent infrared NLO alternative material.
Related work was titled Phase Matching Achieved by Band Gap Widening in Infrared Nonlinear Optical Materials [ABa3Cl2][Ga5S10] (A= K, Rb, Cs), published on CCS Chemistry, associate researcher Liu Binwen was the first author and associate researcher Jiang Xiao Ming and researcher Guo Guocong are corresponding authors.
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