用激光原理和晶体光学原理分析了腔内加旋光晶体时输出光的频差特性。分析表明：当晶片旋转时,理论计算的频差永远小于由晶体两本征模通过晶片位相差所决定的频差,有一特殊因子G2起作用。G2的物理意义是激光本征模在晶体两本征模上的投影比的平方。这表明一个激光本征模在通过晶体时是部分以快模形式,部分以慢模形式,实际位相延迟介于两者之间。由于两者都介于快模和慢模之间,因而实际频差小于由快模和慢模决定的频差。理论计算同实验符合得很好。从而解决了这一多年没有解决的问题。

The beat frequency characteristic of a He-Ne laser with an activity plate in its cavity is studied. The laser physics and crystal optics are used to solve the problem. One mode of laser splits into two eigenstates of crystal as it transmits in the plate. G is the ratio of them, so the time delay of the mode is between those of two eigenstates. The time delay of another mode is also between those of them. So that, the beat freauency is always less than what is determined by the phase difference of two eigenstates. It is related to the special factor G2. Theoretical result matches the experiment very well.