为了研究电场一定时, 光束在非近轴条件下铌酸锂晶体的电光效应, 采用折射率椭球张量的循环坐标变换方法, 理论上推导了光轴正交截面上折射率分布的解析式, 讨论了折射率、相位延迟以及透射率与光束入射方向之间的关系, 并且进行了实验验证, 取得了透过率随光束与光轴夹角α的实验数据。结果表明, y方向加电场时, 入射光小角度偏转将引起x方向感应折射率以及光束透射率的明显变化, 而y方向的感应折射率不变; 光束与光轴的夹角α对铌酸锂晶体电光性能的影响远远大于光矢在x-y平面与x轴正半轴的夹角β对其的影响; x方向加电场时感应折射率同y方向加电场时类似,但此时相位延迟更小, 在0°~0.4399°夹角范围内, 前者的透过率变化较后者慢, 并且在0.45°之后呈现出交替变化的规律, 当夹角为0.5°,0.680°等位置时,它们具有相同的透过率。这一结果对利用角度调节以改善铌酸锂晶体的电光性能具有一定的指导意义。

In order to study the electro-optical effect of LiNbO3 crystal under condition of non-paraxial when electric field was constant, the cyclic coordinate transformation equation of ellipsoid tensor of refractive index was adopted to deduce the expression of refractive index distribution in the optical axis orthogonal region. The dependence of refractive index, phase delay and transmittance upon the direction of incident laser was discussed. The experimental data of the transmittance changing with α, the angle between light beam and optical axis, were obtained. The results show that when the electric field is applied along y axis, a slight deflection of the incident light will lead to a significant change of the x-direction refractive index and beam transmittance whereas the y-direction refractive index has no change. The angle α between light beam and optical axis affects the electro-optical effect of LiNbO3 crystal far greater than the angle β between light vector in the x-y plane and the positive of x axis. The induced refractive index remains similar when adding electric field both in x axis and y axis but the former phase delay is smaller. The transmittance of the former also has a slower change than that of the latter between 0° and 0.4399°, Moreover, after the angle of 0.45°, the transmittance changes alternately at the positions of 0.5°,0.680°and so on, the transmittances in x axis and y axis are just the same. The result has a certain significance to improve the electro-optical properties of LiNbO3 crystal by means of angle adjustment.