Polarization-independent Beam Splitter Based on Light Reflection by a Uniaxial Crystal Surface, and an Immersion Method for Determining the Crystal's Principal Refractive Indices

Abstract

Abstract Light travelling in an isotropic medium of refractive index n and incident on a uniaxial crystal whose optic axis is parallel to the surface and to the plane of incidence is reflected without a change of polarization when n = N g = (N o N e)1/2, where N o and N e are the crystal's ordinary and extraordinary refractive indices. This is true for all incident polarization states and at all angles of incidence and can be used to design a new polarization-independent beam splitter. For a positive uniaxial crystal (N e > N o), total internal reflection occurs at and above a critical angle equal to arcsin (N o/N e)1/2, so that the incident light beam is deflected without attenuation or change of polarization. When n = N g the reflectance at normal incidence for unpolarized or circularly polarized incident light is a minimum: R 0min = (Na - Ng)/(Na + Ng), where N a = ½(N o + N e). This suggests a liquid immersion method in which n and R 0min determine N g and N a, hence N o and N e of the crystal.