— Bi 4– x Pr x Ti 3 O 12 ( x = 0.4, 0.8, 1.2, 1.6) solid solutions have been prepared by solid-state reactions, via multistep firing of stoichiometric mixtures of their constituent oxides in air at temperatures from 1003 to 1323 K. Their crystal structure has been determined using X-ray diffraction, and their luminescence spectra have been measured at room temperature. High-temperature heat capacity of polycrystalline substituted bismuth titanate samples has been determined by differential scanning calorimetry. The C p ( T ) curves of the solid solutions with x = 0.4 and 0.8 have extrema related to phase transitions. Experimental data have been used to calculate the main thermodynamic functions of the solid solutions.

The transmittance anisotropy of a composite polymer-liquid-crystal film has been studied as it varies with the degree to which it is elongated. The composite film includes polyvinyl alcohol, the nematic liquid crystal 4-n-pentyl-4'-cyanobiphenyl, and the surfeiting cetyltrimethylammonium bromide, which initiates homeotropic adhesion of the nematic to the surface of the polymer. It is shown that, when the film is uniaxially stretched, the transmittance of the orthogonally polarized component of directly transmitted radiation and accordingly the degree of polarization abruptly increase, reaching saturation when it is stretched to twice its length. Such variation of the film's macroscopic optical properties can be caused by an orientational-structural transition to a homogeneous configuration of the director in deformed droplets of the nematic and makes it possible to substantially improve the optical characteristics of light polarizers based on such composite media. (C) 2014 Optical Society of America.

Light transmission through a Fabry-Perot resonator (FPR) holding a dielectric cylinder rod is considered. For the cylinder parallel to mirrors of the FPR and the mirrors mimicked by the δ functions we present an exact analytical theory. It is shown that light transmits only for resonant incident angles, α(m), similar to the empty FPR. However after transmission the light scatters into different resonant angles, α(m'), performing resonant angular conversion. We compare the theory with experiment in the FPR, exploring multilayer films as the mirrors and glass cylinder with diameter coincided with the distance between the FPR mirrors. The measured values of angular light conversion agree qualitatively with the theoretical results.

The temperature dependence of the optical transmission spectrum of a one-dimensional multilayer photonic crystal structure with a central defect layer has been studied. The defect was represented by a nematic liquid crystal (5CB) layer with a homeotropic orientation. It is shows that the defect modes exhibit a 10-nm spectral shift due to a change in the refractive index of the liquid crystal in the course of heating-induced transition to the isotropic phase. A comparison of the experimental data to the results of heating-induced transition to the isotropic phase. A comparison of the experimental data to the results of numerical analysis shows the importance of allowance for the decay of defect modes.

Transmission spectra of a one-dimensional photonic crystal (PC) formed by two multilayer dielectric mirrors and a planar oriented layer of 5CB nematic liquid crystal (LC) that is sandwiched between these mirrors and serves as a structure defect are investigated experimentally. Specific features of the behavior of the spectrum of defect modes as a function of the angle of incidence of light on the crystal are studied for two polarizations: parallel and perpendicular to the director of the LC; the director either lies in the plane of incidence or is perpendicular to it. It is shown that, for the configurations considered, the maxima of the defect modes shift toward the short-wavelength region as the tilt angle of incidence radiation increases; this tendency is more manifest for the parallel-polarized component, when the director lies in the plane of incidence. In the latter case, the width of the photonic band gap (PBG) appreciably decreases. The temperature dependence of the polarization components of the transmission spectra of a PC is investigated in the case of normal incidence of light. The spectral shift of defect modes due to the variation of the refractive index of the LC at the nematic-isotropic liquid phase transition point is measured. It is shown that, in real PCs, the amplitude of defect modes decreases when approaching the center of the band gap, as well as when the number of layers in the dielectric mirrors increases. Theoretical transmission spectra of the PCs calculated by the method of recurrence relations with regard to the decay of defect modes are in good agreement with experimental data.

The polarized transmission spectra of the one-dimensional photonic crystal with a planar aligned nematic liquid crystal defect layer have been studied theoretically and experimentally. An effect of the oblique incidence of the light, as well as the temperature of the defect layer, on the spectral positions of the defect modes has been investigated. It is shown that an increase of the incidence angle results in the shift of the defect modes to short-wave range and this tendency appears more pronounced for TM polarization. The spectral shift of the defect modes at 20 nm due to the change of refractive index of the liquid crystal at heating to the isotropic phase was exhibited. The theoretical dependencies of transmission spectra of photonic crystal under study agree well with the experimental data.

The polarized transmission spectra of the one-dimensional photonic crystal with a planar aligned nematic liquid crystal defect layer have been studied theoretically and experimentally. An effect ofthe oblique incidence ofthe light, as well as the temperature of the defect layer, on the spectral positions of the defect modes has been investigated. It is shown that an increase of the incidence angle results in the shift of the defect modes to short-wave range and this tendency appears more pronounced for TM polarization. The spectral shift of the defect modes at 20 nm due to the change of refractive index of the liquid crystal at heating to the isotropic phase was exhibited. The theoretical dependencies of transmission spectra ofphotonic crystal under study agree well with the experimental data.

Temperature dependence of the transmission spectrum of one-dimensional multilayer photonic crystal with a liquid crystal defect layer has been studied. Dielectric multilayers have been fabricated by deposition of an alternating stack of SiO2 and ZrO2 layers on the glass substrate. Homeotropic layer of nematic liquid crystal 5CB is introduced between two multilayers as a defect of the periodic structure. The photonic crystal under study forms the first photonic bandgap in the visible range of the transmission spectrum with a set of the localized modes which number and positions are determined by properties of the defect layer and multilayer dielectric mirrors. The red shift of the defect modes about 10 run has been observed at the nematic-isotropic phase transition. The defect modes positions calculated by the transfer matrix method are in a good agreement with experimental data

In the UV and visible radiation regions, the absorption spectra of α‐Al2O3:Ti,Fe single crystals grown under oxidizing conditions by the Verneuil method are investigated. A considerable residual absorption in the regions 200–300 and 400–600 nm is revealed, which depends strongly on the conditions of growing (the growth rate and temperature drops) and which is caused by transitions in an impurity‐vacancy complex with charge transfer (IVC CT) O2−–Ti4+...Fe3+ and by conversion of the state of titanium ions Ti4+ ↔ Ti3+. The reversible conversion of the state of titanium ions Ti3+ ↔ Ti4+ on bending strain of specimens is established.

Nonlinear optical generation of the third harmonic in the vapour of a metal at a frequency close to the tripled frequency of an iodine laser was achieved for the first time. Phase-matching conditions in the presence of a buffer gas and the nonlinear susceptibility were close to the calculated predictions. A change in the energy of the third-harmonic pulses with time was observed in a cell with cooled windows and a mechanism explaining this effect was proposed. The effect could be eliminated in an all-heated cell with better operational characteristics.