Marina M. Firsova

Congruently melting compositions in the series of solid solutions R1 − xSrxF3 − x (R = La-Nd, 0 ≤ x ≤ 0.15) with tysonite structure (Refinement by directional crystallization)

Congruently melting compositions in the series of solid solutions R1 − xSrxF3 − x (R = La-Nd with a defect structure of the tysonite type (LaF3) were found by the comparing the densities (determined by hydrostatic weighing) of the top and bottom parts of the single crystals grown using the Bridgman method. Measurement errors are analyzed.

Spectrophotometrical method of ordering estimation for liquid crystal in an electro-optical cell

The present work is devoted to the order parameter S estimation in the comb-shaped liquid crystal polymer thin films. The plymer under study was placed in the electrooptical cell and its homeotropical orientation was realized by the action of electrical field between the electrodes. The polarization absorption spectra of the empty cell and the cell with polymer were investigated at different incidence angles of the light beam. The method of interferometric extremum envelopes was used for the processing of the quasiperiodical absorption spectra observed. This method gives the possibility to obtain the optical parameters of the cell electrodes and to re- establish the true polarization spectrum of the polymer film. The polymer order parameter S was calculated from the dichroic ratio for the polymer absorption band at revealed (lambda) = 405 nm. The refractive index dispersion data obtained for the substrates and the polymer from the independent measurements were used for this purpose. The effects of the local field on the order parameter value were also taken into account.

Technique of CeF3 impurity concentration control in LaF3 crystals by means of the UV absorption spectra

The presence of impurities in the crystals has an important influence on their properties. A sensitive method of the impurity control in the crystals without their destruction is the investigation of their absorption spectra. In this work we have studied the LaF3 tysonite crystals widely used as the laser matrices. The LaF3 crystals were grown from the melt by Bridgman-Stockbarger method using the reagents with trade mark high pure and chemical pure. The crystal absorption spectra were recorded in the range of 200-300 nm and the obtained results have shown that the crystals grown from the high pure reagents had no absorption bands in the UV region and the crystals grown from the chemical pure reagents had well defined characteristic absorption bands at (lambda) = 205, 218, 235, 248 nm. Spectral experiments have confirmed the assumption that the UV-absorption bands in the latter crystal samples were caused by the presence of CeF3 impurity in the chemical pure reagents. A technique was developed for evaluation of CeF3 content in LaF3 crystals and in chemical pure mixture of LaF3 with the accuracy +/- 0.0005 mol.%.

Order parameter evaluation of LC polymer from interferometric/refractometric data

The temperature dependence of refractive indices of homeotropically oriented comb-shaped polymer films was determined with the help of optical interference wedge method. For order parameter S(T) estimation from the refractometrical data the information about the temperature dependence of the polymer density is needed and it is also necessary to choose a local field model. Born expression for the molecular refraction invariant in the large temperature range was used for evaluation of the polymer density temperature dependence. The problem of local field effects was investigated in detail on the example of the low-molecular LC PAA. It was shown that for the relative order parameter S(T) estimation it was possible to use Hallers extrapolation method. In this case the results obtained for different local field models are close to one another and to the results obtained by other independent methods.

Method of order parameter estimation for liquid crystal in the electro-optical cell from absorption band dichroism

In this work the polarization absorption spectrum of homeotropically oriented comb-shaped liquid crystal polymer (LCP) film interposed in the electro-optical cell was investigated. The optical parameters of electrodes were estimated from the observed absorption spectra of the cell with and without polymer film using the method of interferometric extrema envelopes. This method enabled us to re-establish the true polarization absorption spectrum of the polymer. For this purpose the refractive index dispersion data of the substrates and the polymer obtained by independent investigation were used.

Optical transmission spectra of Na0.4R0.6F2.2 single crystals with fluorite structure

Na0.4R0.6F2.2 single crystals with fluorite structure were grown by the Stockbarger method. Optical transmission spectra were recorded on the 2 mm thick samples of these crystals at room temperature in the broad spectral region (0.2 - 12 micrometer). It was found that the spectra of crystals with Dy, Ho, Er and Tm ions have the clearly defined discrete structure with a large number of absorption bands in visible, UV and nearest IR regions. The spectra become simpler on going from Dy to Yb. The spectra of crystals with Y and Lu are simplest, almost coinciding and similar to the NaF-crystal spectrum. The peculiarities of these spectra are due to the REE-ions presence in crystalline structure. All single crystals studied have the IR absorption edge at (lambda) approximately equals 12 micrometer. The spectra obtained are compared with these of other fluorides.

Optical rotatory power of trigonal quartz and germanium dioxide single crystals

The optical activity of single crystals of trigonal quartz and its structural analog germanium dioxide, is studied with the help of photoelectric polarimeter. The rotatory power was recorded in the wavelength range 633-365 nm accurate to +/- 0.02 deg/mm. Our experiments showed that the value of rotary power (curly phi) for germanium dioxide was 1.5 times greater than that of quartz, and therefore, the former is more promising in optical applications. The dispersion dependencies of the rotatory power for crystals under study analyzed within the framework of the Chandrasekhars model allowed us to estimate the wavelengths of the fundamental absorption bands that amount to approximately 0.1 micrometers for both objects. The effect of reactor irradiation on the rotatory power of quartz was also examined. These investigations showed that (curly phi) decreases with an increase in the dose, vanishing at 1020 n/cm2. This fact is due to the local irradiation damage of quartz lattice and its gradual amorphization. It should be noted that the value of the characteristic wavelength for the irradiated quartz does not change within the whole dose range studied. This fact provides an evidence that the silicon-oxygen tetrahedron remains as a structural unit of quartz even in its matemict phase.