Birefringence

Summary

Birefringence is the property of a material whose refractive index depends on the polarization and the direction of the light. It comes from an anisotropic permittivity tensor, as in crystals such as calcite and quartz. A beam that enters a birefringent material generally splits into two beams with orthogonal polarizations. Birefringence is the basis of wave plates, polarizing prisms and phase matching in nonlinear optics.