Polarization-dependent group velocity of light pulses traveling in the optic ray axis directions of a biaxial crystal.

We theoretically prove that the group velocity of a light pulse traveling in an optic ray axis direction of a biaxial crystal depends on the polarization state of the light. Our calculation shows that the group index varies as a sinusoidal function of twice the polarization angle of the light pulse. For monoclinic and triclinic crystals, in general the four directions of the two optic ray axes need to be distinguished. Numerical examples show that in KNbO the group velocity varies by 2.7% at 400 nm wavelength, and in SnPS it varies by 3.9% at 550 nm wavelength, when the polarization state of the light is changing.