Nonlinear optical properties and polariton scattering spectra of Ba(NO2)2·H2O crystals

Uniaxial barium nitrite crystals were grown from an aqueous solution and the dispersion of the ordinary and extraordinary refractive indices was determined in the wavelength range 0.44–1.15μ. It was found that the phase-matching conditions could be satisfied in this crystal for generation of the second harmonic of the radiation emitted from a YAG:Nd³⁺ laser. The nonlinear coefficient of barium nitrite (BN) was determined relative to the nonlinear constant of lithium iodate (LI): d₃₁^BN=(0.16±15%)d₃₁^LI. The spectra of the parametric scattering of light by polaritons were determined when these crystals were excited with argon laser radiation. The scattering spectra included a manifestation of the polariton Fermi resonance. The main features of these spectra were interpreted.