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 frequency difference characteristics of the output light are analyzed by using the laser principle and the crystal optics principle. The analysis shows that when the wafer is rotated, the frequency difference of the theoretical calculation is always less than the frequency difference determined by the phase differences between the two eigenmodes of the crystal, and a special factor G2 plays a role. The physical meaning of G2 is the square of the projection ratio of the laser eigenmodes on both eigenmodes of the crystal. This indicates that a laser eigenmode is partially in fast mode when passing through the crystal, partially in slow mode, and the actual phase delay is in between. Since both are between fast mode and slow mode, the actual frequency difference is less than the frequency difference determined by fast mode and slow mode. The theoretical calculation is in good agreement with the experiment. This solved the problem that has not been solved for many years.