Optical characterization of a uniaxial material by the polarization-conversion reflectivity technique

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Abstract
The angle-dependent reflectance at the boundary between an isotropic and a uniaxial material has been fully analyzed, and as a consequence a new technique for complete characterization of the optical tensor of a uniaxial crystal has been developed and demonstrated. For the general uniaxial case, for both positive and negative uniaxial crystals both analytic formulation and numerical modeling show that if the TE-to-TM conversion reflectivity is measured then two sharp cusps appear at critical angles that correspond to the limits of generation of the ordinary and the extraordinary modes in the uniaxial crystal. (For the more conventional polarization-conserving reflectivity there is only one sharp critical edge, the second critical edge being rounded owing to polarization conversion.) It is also found that, for a general orientation of the uniaxial axis with respect to both the plane of incidence and the crystal surface, rotating the plane of incidence by 180° results in a different polarization-conversion signal, thereby permitting a completely unambiguous determination of the Euler angles of the optical tensor. Based on the analytic and numerical modeling results, a novel and accurate optical technique, the polarization-conversion reflectivity technique, has been developed and used to characterize the optical tensor of a single crystal of calcite. The results show that, as well as an accurate optical-tensor characterization, a precise determination of the axis of symmetry of the crystal is simple without recourse to x-ray diffraction.