Universal Method for Determining the Principal Optical Indicatrix Axes in Triclinic Crystals

Abstract

Determining the orientations of principal optical indicatrix axes is a key prerequisite for the applications of optical crystals, which is still an intriguing challenge for triclinic optical crystals due to the lowest symmetry. The prism method is one of the important ways to determine these directions, but no actual examples are available owing to the complexity and scarcity of the triclinic crystals so far. To solve this remaining problem among seven crystal systems, we proposed a universal method, the so-called “multiple prisms method,” to determine the orientations of principal optical indicatrix axes X, Y, and Z as well as the principal refractive index values n x , n y , and n z in triclinic crystals based on four prisms and demonstrated this method by employing triclinic Nd3+-doped La2CaB8O16 crystals, which is of great significance to the studies and applications of triclinic optical crystals in the future.

A Modified Method for Determining the Optical Indicatrix in Monoclinic Crystals Based on Optical Prisms

“…Inspired by the “multiple prisms method” aiming at solving optical indicatrix in a triclinic system, an extra optical prism can also be introduced in the research of monoclinic crystals to modify the conventional method. As seen in Figure , besides the aforementioned two optical prisms (coded “ 1 – 2 ”), an extra prism (coded “ 3 ”) with a light incidence plane parallel to the (100) crystallographic plane can be introduced, which can measure the refractive index values along the b axis (principal refractive index n y ) and c axis (defined as “ n c ”).…”

“…Herein, the correspondences between the two sets of measured refractive index values and n y & n a can not be determined, and polarization directions of emergent lights should be recorded to distinguish n y & n a . The ellipses in (010) cross-planes of optical indicatrix ellipsoid were depicted in Figure 1 Inspired by the "multiple prisms method" aiming at solving optical indicatrix in a triclinic system, 12 an extra optical prism can also be introduced in the research of monoclinic crystals to modify the conventional method. As seen in Figure 2, besides the aforementioned two optical prisms (coded "1−2"), an extra prism (coded "3") with a light incidence plane parallel to the (100) crystallographic plane can be introduced, which can measure the refractive index values along the b axis (principal refractive index n y ) and c axis (defined as "n c ").…”