REFRACTOMETRY OF UNIAXIALLY COMPRESSED Rb2SO4 CRYSTALS

Introduction. The refractive index of a crystal is its fundamental characteristic. In the presence of the experimentally obtained dispersion n ( λ ) with high accuracy, it is possible to determine the fundamental characteristics of single crystals using analytical relations for the refractive index in the region of crystal transparency. Materials and Methods. In this work, high-optical-quality rubidium sulfate (Rb 2 SO 4 ) single crystals were synthesized, crystallographic orientation was determined using a polarization microscope and conoscopic figures, and the dispersion of the refractive indices n x ( λ ) was studied using the Obreimov immersion method at room temperature for different directions of uniaxial compression with stress magnitude of σ m ~ 100 bar. Results and Discussion. It was found that the refractive indices dispersion of this crystal n i ( λ ) is normal ( dn/d λ < 0 ). As the fundamental absorption edge is approached, it increases sharply for the three polarization directions of the electromagnetic wave. The refractive indices satisfy the inequalities n x >= n z > n y and d n x / dλ > dn z / dλ > d n y / dλ . The baric changes in the molar refraction R i , electronic polarizability a i (for the wavelength λ = 500 nm), and crystal-optical parameters (spectral positions of the effective centers of ultraviolet and infrared oscillators, as well as their effective strengths) of Rb 2 SO 4 crystals at room temperature were calculated. It was found that uniaxial pressures of σ ~ 100 bar led to an increase in electronic polarizability of the crystal by an average of (1 – 3)×10 –26 cm 3 . Conclusion. It was established that uniaxial pressures lead to an increase in contributions from infrared oscillators by 2–5 %, primarily due to the baric dependence of the optical isotropic point. They also shift the position of the effective strength of the ultraviolet oscillator λ 0i toward the short-wavelength region of the spectrum. The change in the effective oscillator strength in this baric range does not exceed 1 %. It was found that the positions of effective absorption bands are more sensitive to uniaxial pressures than the effective strengths of the corresponding oscillators. Keywords : refractive indices, uniaxial compression, refraction, electronic polarizability, band gap width.