Because of the difference between the extraordinary and ordinary indices of refraction of the crystal,after passing the crystal,the two orthogonally polarized impulses will be different in phase.

• 光线正入射到这一系统，通过起偏振器后的偏振光投射到晶体上时分解为互相正交的寻常光和非常光，两束光由于折射率的不同经过晶体时会有一定的位相差。