Piezo-optical properties and infrared spectra of Rb2SO4 crystals

The paper deals with the dispersion dependences of birefringence Δn_i(λ) of the mechanically free and uniaxially clamped Rb₂SO₄ crystal along different crystal-physical axes at room temperature. It was found that the crystal has an insignificant normal dispersion d(Δn_x)/dλ χ ≤ 0, and uniaxial compressions σ_m do not change the character, but only the slope of the dependences Δn_i(λ). Uniaxial loads shift the position of the optical isotropic point both in the short-wavelength (σ_z) and in the long-wavelength part of the spectrum (σ_y). The spectral dependences of the combined piezo-optical coefficients ${\pi }_{km}^o\left(\lambda \right)$ were calculated and it was found that they have an insignificant dispersion dependence, and the absolute values of the piezo-optical coefficients ${\pi }_{31}^o$ and ${\pi }_{21}^o$ are equal to each other in the vicinity of the optical isotropic point at the light wavelength λ = 490 nm. The reflection spectra of Rb₂SO₄ crystals were measured in the infrared range at room temperature using FT-IR spectrometer and synchrotron radiation and the corresponding ab initio calculations of the phonon partial density of states and the dielectric function were performed.