POLARIZATION-INDEPENDENT BEAM SPLITTER BASED ON LIGHT-REFLECTION BY AUNIAXIAL CRYSTAL-SURFACE, AND AN IMMERSION METHOD FOR DETERMINING THECRYSTALS PRINCIPAL REFRACTIVE-INDEXES

Light travelling in an isotropic medium of refractive index n and inci dent on a uniaxial crystal whose optic axis is parallel to the surface and to the plane of incidence is reflected without a change of polari zation when n = N(g) = (N(o)N(e))1/2, where N(o) and N(e) are the crys tal's ordinary and extraordinary refractive indices. This is true for all incident polarization states and at all angles of incidence and ca n be used to design a new polarization-independent beam splitter. For a positive uniaxial crystal (N(e) > N(o)), total internal reflection o ccurs 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 chan ge of polarization. When n = N(g) the reflectance at normal incidence for unpolarized or circularly polarized incident light is a minimum: R 0min = (N(a) - N(g))/(N(a) + N(g)), where N(a) = 1/2(N(o) + Ne). This suggests a liquid immersion method in which n and R0min determine N(g) and N(a), hence N(o) and N(e) of the crystal.