Temperature-and-Spectral Deformations of the Optical Indicatrix of Rubidium Sulphate Single Crystal

Abstract

The paper deals with newly investigated temperature-and-spectrum dependences of principal birefringences (∆ni(λ, T )–i = X, Y , Z; λ = 250 ÷ 850 nm; T = 4.2–1100 K), and temperature dependence of the optic-axial angle (2V (T ) — T = 4.2–1100 K) for two laser lines 632.8 nm and 441.1 nm of Rb2SO4 crystals. Based on the temperature dependence of the optic-axial angle, the second point of birefringence sign inversion has been found. Newly obtained is the temperature-and-spectrum diagram of the uniaxial state of the optical indicatrix at the “isotropic points” and in the hexagonal phase of Rb2SO4. Based on the temperature behavior of the birefringence and optic-axial angle it was supposed that hexagonal-orthorhombic phase transition in rubidium sulfate can be a second-order phase transition. Found is the inversion of birefringence dispersion in the X and Y directions at 400 K and 620 K, respectively.