Effective magnetic properties of a composite material with circular conductive elements

Effective magnetic properties of a composite meta-material consisting of periodically arranged circular conductive elements are studied theoretically. A general expression for the effective bulk permeability is obtained with mutual effects and lattice ordering being taken into account. The resonance frequency of the permeability is found to be strongly dependent on the size and shape of the unit cell. Frequency dispersion of the permeability is studied with special attention paid to the frequency range, where negative values of the permeability are possible. Corresponding recommendations for optimisation of the meta-materials with negative permeability are made. The results are confirmed by numerical simulations of the finite structure behaviour in an external magnetic field. Received 19 April 2002 Published online 31 July 2002     

Theory of periodic states for feedback-controlled photorefractive nonlinear systems

Certain feedback loops can be used in photorefractive optical schemes to implement periodic states and create spatial gratings characterized by extremely high or low diffraction efficiencies. This highly nonlinear phenomenon is studied both experimentally and numerically. An analytical method is developed for analyzing periodic states with the use of symmetries of time-dependent diffraction equations and fast feedback response. The method is applied to describe the properties of periodic states, including their spatial structure, diffraction-efficiency oscillation period and amplitude, and characteristics of feedback-controlled strong phase modulation.     

Model‐independent structure and resonant X‐ray spectra of intermediate smectic phases

It is shown that the orientational structure of intermediate smectic phases can be determined using the symmetry properties of the general free energy with arbitrary orientational coupling between smectic layers, without addressing a particular model. The structure of three‐ and four‐layer intermediate phases, obtained in this way, corresponds to experimental data. The same method enables one to predict the structure of intermediate phases with periodicity of five and six layers, which have not been observed experimentally so far. The resonant X‐ray spectra of the five‐ and six‐layer intermediate phases with predicted structure have also been calculated. These spectra are characterized by a number of features which enable one to distinguish five‐layer and six‐layer intermediate phases from phases with smaller periods.     

Feedback-controlled two-wave coupling in reflection geometry: application to lithium niobate crystals subjected to extremely high external electric fields

An active stabilization of photorefractive two-wave coupling by means of an electronic feedback loop has been used extensively during recent years in transmission geometry. It leads to 100% diffraction efficiency and also to periodic states instead of familiar steady states. We investigate the feedback operation in the case of reflection geometry, especially for iron-doped lithium niobate (LiNbO₃:Fe) crystals. This includes formulation of the feedback equations, numerical analysis of the operation regimes for LiNbO₃ crystals, and comparison between theory and experiment, which is performed in the range of applied electric fields from 0 to 650kVcm^-1. The main findings are as follows: (i) the feedback does not lead to periodic states, (ii) it modifies the photorefractive response by introducing a frequency shift and maximizes , and (iii) there is a close relation between the enhancement of and the resonant excitation of space-charge waves predicted earlier in ferroelectric materials. PACS 42.40.Ht; 42.65.Hw     

A Study of Laser Photoionization of 177mLu Nuclear Isomer

Optics and Spectroscopy - The hyperfine structure of transitions of the three-step photoionization scheme of lutetium, 5d6s2 2D3/2−5d6s6p 4F$$_{{5/2}}^{^\circ...     

Plasmon electro-optic effect in a subwavelength metallic nanograting with a nematic liquid crystal

The electro-optic effect in hybrid structures based on subwavelength metallic nanogratings in contact with a layer of a nematic liquid crystal has been experimentally studied. Metallic gratings are fabricated in the form of interdigitated electrodes, which makes it possible to use them not only as optical elements but also for the production of an electric field in a thin surface region of the layer of the liquid crystal. It has been shown that, owing to the electric-field-induced reorientation of molecules of the liquid crystal near the surface of the grating, it is possible to significantly control the spectral features of the transmission of light, which are caused by the excitation of surface plasmons. The electro-optic effect is superfast for liquid crystal devices because a change in the optical properties of the system requires the reorientation of molecules only in a very thin surface layer of the liquid crystal.     

Deceleration and shape-transformation of light pulses during?phase conjugation in photorefractive media

We have theoretically investigated the main features of pulse deceleration and pulse-shape transformations during phase conjugation in photorefractive nonlinear media. The main attention in article is paid to the critical features which occur near the threshold of mirrorless oscillation. It is shown that the effects of critical enhancement when approaching the threshold do not lead to superior light slowing down characteristics as compared to the case of two-beam coupling. At the same time, essentially new features of pulse-shape transformation occur above the threshold.     

Electromagnetic properties and structure of polydisperse mechanically activated Fe-Si materials

Complex investigation of the physical properties and structure of sintered powder materials of the Fe-Si system after grinding of a mixture of powders in two different mechanical aggregates has been performed. It is shown that fragmentation of powders in both a BW-micro vibration grinder and in a Fritsch-type centrifugal planetary mill leads to a nonmonotonic change in the properties of sintered materials. This result is explained by mechanical activation of powders during grinding. Original Russian Text ? G.A. Dorogina, I.A. Kuznetsov, E.S. Gorkunov, Yu.V. Subachev, 2009, published in Izvestiya Rossiiskoi Akademii Nauk. Seriya Fizicheskaya, 2009, Vol. 73, No. 1, pp. 141–144.     

Magnetoelastic acoustic emission in ferrosilicon single crystals

The influence of magnetic-reversal effects on magnetoelastic acoustic emission (MAE) in single crystals of Fe + 3% Si cut in the [100], [110], and [111] directions is investigated, along with the relationship of these signals to the linear magnetostriction. It is shown that the MAE signals depend on the crystallographic directions and exhibit processes associated with rearrangement of the 90° domains throughout the entire volume of the ferromagnet.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 62–66, January, 1986.