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Raman scattering (RS) spectra in lithium tantalate single crystals are studied at 180-degree scattering geometry in a wide frequency spectral range (50–2500 cm–1). RS intensity peaks corresponding to fundamental transverse (TO) and longitudinal (LO) polar optical modes of this crystal are recorded. It is found that the high-frequency spectral range (1300–2000 cm–1) contains RS intensity peaks whose frequencies exceed doubled frequencies of A1- and E-type fundamental vibrations of the LiTaO3 lattice. The intensity of these peaks appeared comparable to the intensity of lines corresponding to A1- and E-type fundamental transverse and longitudinal polar optical modes. The conditions of the appearance of bound states of polar phonons in the RS spectra of lithium tantalate crystal are analyzed.

An increase in the intensity of photoluminescence spectra of organic phosphor with terbium Tb3+ ions intruded into a 3D photonic crystal, i.e., SiO2 opal matrix, is established. The superluminescence effect is observed upon excitation at a wavelength of 369 nm at the 5D4–7F5 transition in Tb3+ ion in the green spectral region (λ = 545 nm). Lasing feasibilities in the composite opal matrix for the 5D4–7F5 transition in Tb3+ ion are analyzed.

The dispersion relations of exciton polariton waves in terbium nitrate hexahydrate are determined based on the model of the interaction of electromagnetic waves with resonant electronic states of Tb3+ ions at the 5D4–7F6 transition. Frequencies of unitary polaritons characterized by refractive indices equal to unity are determined. It is shown that the group velocity of electromagnetic waves in the region of unitary polaritons is lower than the speed of light in vacuum by several orders of magnitude. A sharp increase in the efficiency of photoluminescence and Raman scattering is predicted in the case where the excitation radiation frequency approaches the unitary polaritons frequency.

The possibility of generating and detecting high-frequency gravitational waves based on nonlinear-optical processes in dielectric media at their excitation by intense laser radiation of visible or ultraviolet ranges is analyzed. The theory predicts the feasibility of the Hertz gravitational laboratory experiment in which the parametric conversion of intense laser radiation with frequency ω0 = 2πf0 (f0 = 1014 − 1015 Hz) to a gravitational wave with frequency ω g = 2ω0 and the reverse process of gravitational radiation reconversion to optical radiation are implemented in the condensed dielectric medium.

Spectral characteristics of stimulated Raman scattering at least in synthetic opal matrices infiltrated with liquid nitrogen upon excitation by nanosecond laser pulses are studied. The effect of the stop band position on the generation efficiency of anti-Stokes components of stimulated Raman scattering up to the third order is demonstrated. The excitation threshold of stimulated Raman scattering in liquid nitrogen infiltrated into opals is significantly lower in comparison with the generation in bulk samples.

The systematic features in the reflectance spectra of broadband optical radiation from the surface of one-dimensional photonic crystals based on mesoporous structures are presented. The dispersion dependence for electromagnetic waves in the mesoporous one-dimensional photonic crystal is established. On its basis, reflectance and transmittance spectra are calculated for particular structures, and the microscopic parameters of the samples under study are determined. The developed theory is used to explain the shape of reflectance spectra in mesoporous photonic crystals based on silicon, quartz, and aluminum oxide.