Interference of nonpolarized light in liquid crystal domains on the polymer surface

The interference of the nonpolarized light transmitted through an ensemble of nematic liquid crystal domains formed on the polycarbonate surface has been investigated. A model based on the superposition of the ordinary and extraordinary beams passed through domains with the radial structure has been developed. Expressions for the phase difference and intensity of the interfering beams, which take into account the distribution of the liquid crystal director field, have been derived. The dependences of the optical transmittance of a domain layer on the applied voltage have been calculated with regard to the material and optical constants of a liquid crystal and structural features and averaged morphological parameters of individual domains in the experimental sample. The results of the calculation are consistent with the experimental data, which confirms the validity of the proposed model

Optical spectra of the triplet He-2* excitations in various phases of liquid He-3 and He-4 under high pressures

Measurements of the a --> c and a --> b absorption bands have been carried out in normal He-4 and He-3 under various pressures and temperatures. We have found that the blue shift of the a --> c increases with the pressure and with the particle density of the liquid in accordance with the "bubble" model. We have studied changes in the characteristics of the spectra at the superfluid transition. It was found that the width of the (0-0) a --> c absorption line strongly increases with the temperature. (C) 2000 Elsevier Science B.V. All rights reserved

Structure and dynamics of the He-2(*) (a3 Sigma(+)(u)) molecular complex in condensed phases of helium

An investigation is made of the absorption spectra of triplet metastable helium molecules in the a(3) Sigma (+)(u)state in liquid He-4 and He-3 at various pressures and in dense He-3 gas. An analysis of the spectrum corresponding to the a(3)Sigma (+)(u) --> c(3)Sigma (+)(g) transition confirms the conclusion that there is a microscopic bubble surrounding the molecule in liquid helium. A simple approximation is proposed for the wave function of the valence electron of the molecule and the parameters of the bubble are determined for various experimental conditions. The coefficient of molecular recombination in liquid He-3 and He-4 was determined experimentally at various pressures and in dense cold He-3 gas. The results show good agreement with the theory of mutual recombination limited by molecular diffusion under conditions of strong van der Waals interaction. It is shown that in the condensed phases of helium the polarization of the molecules under the action of the magnetic field does not lead to suppression of their mutual recombination, and this is confirmed experimentally. (C) 2000 MAIK "Nauka/Interperiodica"

Electric and Magnetic Field-Assisted Orientational Transitions in the Ensembles of Domains in a Nematic Liquid Crystal on the Polymer Surface

Using electro- and magneto-optical techniques, we investigated orientational transitions in the ensembles of domains in a nematic liquid crystal on the polycarbonate film surface under the conditions of competing surface forces that favor radial and uniform planar alignment of nematic molecules. Having analyzed field dependences of the intensity of light passed through a sample, we established the threshold character of the orientational effects, plotted the calculated intensity versus magnetic coherence length, and compared the latter with the equilibrium length that characterizes the balance of forces on the polymer surface

Vibrating wire measurements in superfluid He-3 at the melting curve down to 0.53 mK.

Measurements of the vibrating wire spectrum have been carried out in superfluid He-3 along the melting curve down to 0.53mK. We have observed that at temperatures below 0.3 T-c, the width of the mechanical resonance of the wire decreases exponentially with 1/T, indicating the ballistic regime of collisions with quasiparticles, The value of the superfluid energy gap was found to be (1.99+/-0.05) T-c, in good agreement with the values obtained from heat capacity measurements. The vibrating wire was thereby calibrated for further experiments at temperatures below 0.5 mK, where the sensitivity of the melting curve thermometry becomes rather poor

Domain Structures in Nematic Liquid Crystals on a Polycarbonate Surface

Alignment of nematic liquid crystals on polycarbonate films obtained with the use of solvents with different solvations is studied. Domain structures occurring during the growth on the polymer surface against the background of the initial thread-like or schlieren texture are demonstrated. It is established by optical methods that the domains are stable formations visualizing the polymer surface structures. In nematic droplets, the temperature-induced transition from the domain structure with two extinction bands to the structure with four bands is observed. This transition is shown to be caused by reorientation of the nematic director in the liquid crystal volume from the planar alignment to the homeotropic state with the pronounced radial configuration of nematic molecules on the surface. The observed textures are compared with different combinations of the volume LC orientations and the radial distribution of the director field and the disclination lines at the polycarbonate surface

Measurements on the surface tension of He-3 crystals near 100 mK.

He-3 crystals start to show facets on their surface only at about 100 mK, well below the roughening transition temperature, and the reason for this change of the surface state is not clear yet. However, the most important characteristic of the crystal surface, the surface tension, was not measured in this temperature range before. We report our observations on the equilibrium shape of the He-3 crystals in the temperature range of 77...110 mK. The surface tension was found to be isotropic and temperature-independent, and the corresponding value of the capillary length, lambda = 0.93 +/- 0.10 mm, is in a good agreement with the value measured at higher temperatures by Rolley et al

First observation of the critical size of facets on He-3 crystals near 1 mK.

We have been able to obtain the step free energies of the basic (110) and (100) facets on He-3 crystals near 1 mK by using a new method in which the critical radius of facets is measured on slowly melting crystals. The critical radius is obtained by tracking optically the moment that the facet collapses. Our findings confirm that at such low temperatures the liquid-solid interface of He-3 is indeed strongly coupled to the crystal lattice, as was suggested in our previous studies

Faceting of He-3 crystals.

We report on our optical observations on BCC He-3 crystals in the temperature range of 8-55 mK. With our interferometric technique we were able to identify at least three different types of facets, (1 1 0), (1 0 0), and (2 1 1), at temperatures up to 55 mK. Previously, only the (1 1 0) facet was observed at such high temperatures