Static photoelasticity of gallium phosphide crystals

The piezo-optic effect (POE) in cubic GaP crystals (symmetry class [`4]\bar 43m) is studied in detail by interferometry. The relations for determining the absolute piezo-optic coefficients (POCs) π _im or their combinations on a sample of X/45° cut at all allowable geometries of the experiment are recorded. The determination of a specific coefficient π _im at different experimental geometries on samples of right cuts and a X/45° cut made it possible to find the π _im values with a high accuracy and reliability.     

Anisotropy of the electro-optic effect in magnesium-doped LiNbO3 crystals

Specific features of constructing indicatory surfaces of the electro-optic effect (EOE) are described. The generalized case for the symmetry class 3m and all three possible indicatory surfaces under orthogonal experimental conditions, when the directions of light propagation and electric field are orthogonal, is considered. The EOE surfaces are constructed for magnesium-doped lithium niobate crystals. The specific features of anisotropy of these surfaces are discussed and their extreme values and corresponding angular coordinates are found. To construct the indicatory surfaces, all absolute coefficients of the linear electro-optic effect are determined by the interferometric method. The difference in the electro-optic coefficients of pure and magnesiumdoped crystals does not exceed 10%. An advantage of doped crystals is their high durability to high-power laser radiation.

     

Nanostructures on the Basis of Porous Alumina with Intercalated with Cholesteric Liquid Crystal

The introduction of liquid crystal materials into the porous material host will help us to get optically active nanocomposites. Nanocomposite based on aluminum oxide host with cholesteric liquid crystal is characterized by a shift of bandwidth wavelength minimum. In case of intercalation of cholesteric liquid crystals into the pores of aluminum oxide host the shift of transmittance minimum into the short wave region are observed. We analyzed the ways, which indicate the deformation of the pitch of the cholesteric helix and showed the role of capillary forces in the deformation of the pitch of cholesteric liquid crystal.     

On the beam propagation through active media

An analytical iterative procedure has been established to determine the amplitude of a laser beam propagating through an active medium. The treatment is valid for both homogeneous and inhomogeneous broadening, and for arbitrary inhomogeneities of the parameters characterizing the active medium, namely, the refractive index, the small-signal gain and the saturation intensity. After a supplementary approximation, a thin-sheet gain approach is derived from the first iteration. The formalism enables us to provide analytical criteria for evaluating both the accuracy of each iteration and the propagation distances for which the thin-sheet solution can be used. This revised version was published online in November 2006 with corrections to the Cover Date.     

Spatial anisotropy of linear electro-optic effect in crystal materials: I—Experimental determination of electro-optic tensor in LiNbO3 by means of interferometric technique

The paper presents a technique suitable for the determination of linear electro-optic effect (LEOE) tensor components in crystal materials of any symmetry. The method is based on the Michelson interferometer, where the sample being studied is set into one of its arms to measure the electro-induced changes of the optical path. We describe in detail the sample geometries that are needed to determine a complete set of the LEOE tensor components and derive the corresponding equations. The experimental technique has been tested and verified on lithium niobate crystals as well as applied to MgO-doped LiNbO₃ crystals to study their electro-optic properties. The developed method can be useful for optical engineering, which deals with new materials being used in design or production of devices, such as, e.g., modulators or deflectors.     

Spatial characterization of the transversal structure of rotationally symmetric pulsed beams

A simple analytical model is proposed to describe the transversal spatial structure of a tridimensional rotationally symmetric pulsed beam. The spatial behaviour of the pulse amplitude is shown to be linked to its (measurable) second- and higher-order intensity moments, namely, beam width, quality parameter and kurtosis. As an illustrative experimental example, this model has been applied to high-quality TEA CO2 laser pulses. This revised version was published online in November 2006 with corrections to the Cover Date.     

Greatly attenuated experimental autoimmune encephalomyelitis in aquaporin-4 knockout mice

Background  

The involvement of astrocyte water channel aquaporin-4 (AQP4) in autoimmune diseases of the central nervous system has been suggested following the identification of AQP4 autoantibodies in neuromyelitis optica, an inflammatory demyelinating disease.     

Differences Between Consecutive Primes

Let p_n be the nth prime. Then this paper is concerned with provingthe following result on the distribution of consecutive primes. The exponent of x in this theorem improves on the work of Heath-Brownwho proved (1) with exponent . Under the Riemann hypothesisone can prove (1) with exponent .The proof of the theorem startswith the Heath-Brown–Linnik identity which leads to aformula giving the number of primes in an interval in termsof coefficients of certain Dirichlet series. I then estimatethe coefficients by using, among other things, the informationwhich can be gained from Montgomery's mean value theorem andHuxley's version of the Hal' asz lemma. Furthermore, by usingfamiliar sieve arguments I am able to discard some of the coefficientsallowing us to gain an improvement over the previous resultof Heath-Brown. 1991 Mathematics Subject Classification: 11N05.     

The Lithium Niobate Piezooptical Features

Piezooptical effect (POE) in LiNbO₃ crystals is analytically described considering crystallophysical axes of positive directions choice. All the piezooptical coefficients have been determined and correlation of the absolute piezooptical coefficients (POCs) and coefficients, describing stress-induced birefringence, has been carried out. The POE indicating surface sections, which adequately reflect the anisotropy effect, have been constructed.     

Angular stability of electric field‐induced effects in crystalline materials

We analyze angular bandwidths of extrema of the indicative surfaces describing spatial anisotropy of piezoelectric (PE) and electrooptic (EO) properties of doped lithium niobate (LiNbO₃:MgO) and langasite (La₃Ga₅SiO₁₄) crystals. A number of highly efficient experimental geometries are suggested, which are promising for PE and EO devices. Our data obtained with both analytical and numerical techniques characterize angular stability of those devices and, in particular, their angular aperture. We show that, besides of a maximal size of the electric field‐induced effects, ‘nondirect crystal cuts’ offer considerably higher angular stability of their characteristics, when compared with that typical for ‘direct crystal cuts’ usually employed in PE and EO devices.