Shao Z, Yi C
Appl Opt. 1994 Mar 1;33(7):1209-12. doi: 10.1364/AO.33.001209.
We have experimentally investigated the behavior of extraordinary rays (E rays) in uniaxial crystals for two cases: that in which optical axes are parallel to the surfaces and that in which they are inclined. The E ray always rotates around the ordinary ray (O ray) in the same direction that the crystal rotates around its surface normal. For the case when the axes are parallel to the surface, we discovered that the E ray rotates up to α = 2π as the crystal rotates to ? = π. The E ray traces a series of ellipses as the angle of incidence is varied. Snell's law is valid for the E ray only when the optical axes are perpendicular to the plane of incidence. For the case in which the optical axes are incident, the E ray and the crystal rotate at different speeds except for the case of normal incidence. The speed of rotation increases with the incidence angle. The ray traces a curve known as the Pascal worm, which is described by the equation (x(2) + z(2) - mx)(2) = n(2)(x(2) + z(2)). When the optical axes coincide with the plane of incidence, the space between the rays in the plane is not related to the angle of incidence.
我们通过实验研究了单轴晶体中非常光线（E光）在两种情况下的行为：一种情况是光轴与表面平行，另一种情况是光轴倾斜。E光总是围绕寻常光线（O光）沿与晶体围绕其表面法线旋转相同的方向旋转。对于光轴与表面平行的情况，我们发现当晶体旋转到θ = π时，E光旋转至α = 2π。随着入射角的变化，E光描绘出一系列椭圆。只有当光轴垂直于入射平面时，斯涅尔定律才对E光有效。对于光轴倾斜的情况，除了垂直入射的情况外，E光和晶体以不同的速度旋转。旋转速度随入射角增加。光线描绘出一条称为帕斯卡蠕虫线的曲线，其方程为(x² + z² - mx)² = n²(x² + z²)。当光轴与入射平面重合时，平面内光线之间的间距与入射角无关。
