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利用Yb~(3+)∶KGd(WO_4)_2晶体的热膨胀系数各向异性和折射率温度梯度为负值的特点,就可能找到被光抽运时热透镜效应为零的特定方向,此方向即为“无热透镜方向”。鉴于前人的理论计算中存在着一些缺陷,利用最小二乘法和二阶张量旋转法,精确计算了Yb~(3+)∶KGd(WO_4)_2晶体的热膨胀张量以及在不同偏振状态下的无热透镜方向:m偏振时,在p-g平面内与p轴成±46.3°的方向;p偏振时,在m-g平面内与m轴顺时针成24.9°以及与m轴逆时针成81.2°的方向;g偏振时不存在无热透镜方向。将之与前人的计算结果进行了比较,指出了其理论模型中存在的缺陷。计算了p偏振时在m-g平面内与m轴顺时针成17°的方向上传播以及m偏振时b方向传播的单位光程变化值,并与前人已发表的理论与实验结果做了对比分析,证实了所建理论体系的有效性。
Using the anisotropy of thermal expansion coefficient and negative temperature gradient of refractive index of Yb 3+: KGd (WO 4) 2 crystal, it is possible to find the specific direction of thermal lens effect zero by optical pumping. It is “No hot lens direction ”. In view of the defects in the theoretical calculation of the predecessors, the thermal expansion tensor of Yb3 +: KG4 (2) crystal is calculated accurately by using the least squares method and the second-order tensor method, Of the non-thermal lens direction: in the pg plane, in the pg plane, in a direction of ± 46.3 ° to the p-axis when in p-polarization; 24.9 ° in the mg plane clockwise with the m-axis and 81.2 ° counterclockwise to the m- Orientation; g-polarized does not exist without the direction of the thermal lens. Comparing it with the previous calculation results, the defects in the theoretical model are pointed out. The change of unit optical path of p-polarization propagating in the direction of 17 ° from the m-axis and in the direction of m-polarization was calculated and compared with the theoretical and experimental results previously published , Confirmed the validity of the theoretical system built.