Application of Equivalent Air Gap Method in Uniaxial Crystal Plate

The equivalent air gap method is a simple way to trace the ray propagation in an isotropic medium, but it cannot be applied to an anisotropic medium. We present the exact general expressions of the equivalent air gap thicknesses and the displacements for the plane-parallel uniaxial crystal plates. They are also suitable for the isotropic medium. This method is useful when one determines whether certain size plane-parallel plates can be fitted into the available air of an optical system, and also in the prism system design.