THE BASIC PRINCIPLES OF BIREFRINGENT CRYSTAL

各向异性透明晶体如方解石、石英等的折射率，是其固有的特性，称为永久双折射。If the electric discipline has the direction with the optical axis, a person obtains the amazing index ne. This is possible only if the propagation route (more precisely, the course from the k vector) is perpendicular on the optical axis.