依据全反射原理和自准直测角法，实现了对棱镜折射率的精确测量。通过使用高准直半导体激光器将激光入射到棱镜内部与空气分界面上，逐步旋转棱镜或改变棱镜的入射角，得到待测棱镜的反射光强随入射角变化曲线。在曲线左侧收尾处出现一个台阶，其反射光强随入射角增大迅速衰减。全反射临界点，对应的入射角为全反射角。用两次自准直测角法精确测量棱镜底角。通过该方法，分别对两块不同棱镜的折射率进行了测量，测量棱镜折射率精度为±1.24×10-4。

According to the principle of total internal reflection and autocollimator angle measurement method, accurate measurement of the prism refractive index is achieved. By the using of highly aligned semiconductor laser, the laser goes into interface of the prism and air. The curve of the prism′s reflected light versus the incident angle is obtained by rotating prism or changing the prism′s incident angle gradually. A step appears at the left side of the curve ending and its reflected light rapidly attenuates with the increasing of the incident angle, which is the angle of total reflection. The base angle of the prism is accurately measured by the double using of auto collimation angle measurement method. Refractive index of two pieces of different prism is measured by this method, respectively. The measuring accuracy is ±1.24×10-4.