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Saint Petersburg, Russia

Balonin N.,Saint Petersburg State University | Sergeev M.,University of Information Technologies
Frontiers in Artificial Intelligence and Applications | Year: 2014

This article discusses the procedure of image compression using the Hadamard-Mersenne, Hadamard-Fermat matrices and derived from them orthogonal M-matrices. At the stage of image spectral decomposition it is proposed to use the original two-tier symmetric orthogonal M-matrices order, equal to the Mersenne and Fermat primes, as well as the low frequency filters relevant to them. © 2014 The authors and IOS Press. All rights reserved. Source

Ivanov V.S.,University of Turku | Rozhdestvensky Y.V.,University of Information Technologies | Suominen K.-A.,University of Turku
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2014

We present a scheme for high-precision three-dimensional (3D) localization by the measurement of the atomic-level population. The scheme is applied to a four-level tripod-type atom coupled by three strong standing waves and a probe running wave. As a result, the atom can be localized in volumes that are substantially smaller than a cubic optical wavelength, which is achieved by the increase of standing-wave intensities. The upper-level distribution depends crucially on the atom-field coupling and it forms 3D periodic structures composed of spheres, hourglasses, bowls, donuts, or deformed barrels. © 2014 American Physical Society. Source

Rupasinghe C.,Monash University | Rukhlenko I.D.,Monash University | Rukhlenko I.D.,University of Information Technologies | Premaratne M.,Monash University
ACS Nano | Year: 2014

Spaser is a nanoscale source of surface plasmons comprising a plasmonic resonator and gain medium to replenish energy losses. Here we propose a carbon-based spaser design in which a graphene nanoflake (GNF) resonator is coupled to a carbon nanotube (CNT) gain element. We theoretically demonstrate that the optically excited CNT can nonradiatively transfer its energy to the localized plasmon modes of the GNF because of the near-field interaction between the modes and the CNT excitons. By calculating the localized fields of the plasmon modes and the matrix elements of the plasmon-exciton interaction, we find the optimal geometric and material parameters of the spaser that yield the highest plasmon generation rate. The results obtained may prove useful in designing robust and ultracompact coherent sources of surface plasmons for plasmonic nanocircuits. © 2014 American Chemical Society. Source

Sikdar D.,Monash University | Rukhlenko I.D.,Monash University | Rukhlenko I.D.,University of Information Technologies | Cheng W.,Monash University | And 2 more authors.
Plasmonics | Year: 2014

Using the image charge theory and finite element methods, we present the first comprehensive study on the optical properties of substrate-supported, three-layer, metal/dielectric/metal nanospheres. By adopting dipolar and quadrupolar approximations of the quasistatic image charge theory, we derive analytical expressions for the polarization-dependent polarizabilities of a three-layer nanosphere near a substrate and use them to find the nanosphere's plasmon resonance wavelengths as functions of the geometric and material parameters of the nanosphere-substrate system. By calculating the resonance wavelength of substrate-supported gold/silica/gold nanosphere over a sufficiently large domain of the nanosphere's dimensions, we show that this wavelength can be tuned from visible to infrared regions by altering only the size of the nanosphere's core. We also show that the resonance position as well as the enhancement and confinement of the near-field can be dynamically tuned over broad ranges by changing the polarization of the excitation light. Of significance for the applicability of our results in practice is that we employ size-dependent permittivity of gold, which allows experimentalists to readily produce these substrate-supported nanospheres with desired optical responses. Upon comparing our analytical results with the results of numerical simulations, we reveal the range of the nanospheres' outer radii within which the dipolar and quadrupolar approximations adequately describe the nanosphere-substrate interaction. Since majority of the optical functions are realized with light polarized parallel to the substrate, our results allow one to readily engineer the broadband optical responses of substrate-supported metal/dielectric/metal nanospheres for applications in resonance-enhanced sensing, in light harvesting, and in biomedicine. © 2014 Springer Science+Business Media New York. Source

Vakulin D.A.,University of Information Technologies
Technical Physics Letters | Year: 2015

A new technique for determining the director pretilt angle in cells with hybrid or homeotropic alignment of a nematic liquid crystal has been developed. To use this technique, it is necessary to experimentally determine the transmission of an optical system in parallel polarizers and maximum transmission of a cell in crossed polarizers. The technique makes it possible to locally control the liquid crystal director alignment on an aligning surface. © 2015, Pleiades Publishing, Ltd. Source

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