对红外非线性光学晶体CdSe的倍频光学参数及其元件加工进行了研究.根据非线性光学原理和折射率色散关系,从理论上计算出CdSe晶体的有效非线性系数和倍频元件相位匹配角与基频光波长(5.5～10.0 μm)的调谐特性曲线,从实验上探索到一种通过解理试验和XRD定向测试,快速确定其光轴方向的晶体定向新方法.结果表明,CdSe晶体在Ⅱ类相位匹配条件下的有效非线性系数d_(eff)为d_(15)sinθ,倍频转换效率与方位角无关;在Ⅰ类相位匹配条件下其有效非线性系数d_(eff)恒等于0,无倍频输出.根据理论计算结果,运用定向新方法,针对VUVG法生长出的外观无方向特征的CdSe晶体,经定向切割、研磨和抛光,初步加工出基频波长为9.6 μm的CdSe晶体Ⅱ类相位匹配倍频元件, 尺寸达9.5 mm×9.5 mm×18 mm.
The infrared frequency doubles parameters and element processes of CdSe crystals were studied. According to the infrared nonlinear optical theory and refractive index dispersion relation, the tuning curve of angular vs. Fundamental wavelength(5.5-10.0 μm) of the CdSe crystal at 100 ℃ was obtained, and from theory calculation, the azimuth angle of CdSe crystal could be discretionary chosen because it didn't influence the type Ⅱ phase matching effective nonlinearity d_(eff), which equal to d_(15) sinθ. However, calculation results of the effective nonlinearity on the type Ⅰ phase matching condition indicated that effective nonlinearity equal to zero, so CdSe crystal could not realize type Ⅰ frequency doubles. Further, for the CdSe crystal (grown by VUVG method) without any direction characters, based on CdSe crystal structure properties,a fast and new method to determine the optical axis by cleavage and XRD analysis was developed. The crystal was cut directionally, grinded and polished, and a type Ⅱ phase matching element with a size of 9.5 mm×9.5 mm×18 mm for 9.6 μm fundamental frequency was obtained preliminarily.
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