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Yu. V. Rostovtsev

Publications and source records attributed to Yu. V. Rostovtsev.

11 recordsLinked to original sources
arXiv2021

Absorption and Emission Dependences on Defect in CLC

The influence of the defect position on absorption and emission in the cholesteric liquid crystal with an isotropic defect inside is studied. It is shown that for non-diffracting circularly polarized incident light absorption/emission is maximum if the defect is in the centre of the system; and for diffracting circularly polarized incident light absorption/emission is maximum if the defect is shifted from the centre of the system to its left border from where light is incident. The influence of anisotropic absorption in the cholesteric liquid crystal layer on photonic states of density was investigated, too.

physics.optics↗
arXiv2020

On a Positron Channeling in Ionic Crystals

An analytical expression is received for the effective interaction potential of a fast charged particle with the ionic crystal CsCl near the direction of axis <100> as a function of the temperature of the medium. A possibility of positron channeling in this potential is shown. By numerical analysis it is shown that the effective potential of axial channeling of positrons along the axis <100> of negatively charged ions practically does not depend on temperature of the media.

physics.acc-ph↗
arXiv2018

The Influence of Absorption and Gain on Photonic Density of States

The photonic density of states (PDS) of the eigen polarizations (EPs) in cholesteric liquid crystal (CLC) cells are calculated. The exact analytic expressions for the reflection and transmission matrices for the finite thickness CLC layer are used. We obtained the dependences for the PDS on the parameters characterizing absorption and gain, as well as the CLC cell thickness, CLC local dielectric anisotropy and refractive index of CLC layer surrounding. The possibility of connections between the PDS and the density of the light energy accumulated in the medium are investigated and it was shown that these characteristics have analogous spectra and, besides, the influences of the problem parameters on these characteristics also were analogous. We have shown, that the decrement of the refractive index of CLC layer surroundings leads to a sharp increase of the maximum PDS and, consequently, leads to a sharp decrement of the laser excitation threshold. The PDS dependence on the refraction coefficients of the substrates of the Fabry-Perot resonator filled with a CLC planar layer was investigated, too. It is shown that the subject system can work as a low threshold laser or a multi-position trigger.

physics.optics↗
arXiv2017

The Effect of Defect Layer on Lasing in Cholesteric Liquid Crystal

The photonic density of states (PDS) of eigen polarizations (EPs) in cholesteric liquid crystal (CLC) cells with a defect layer inside are calculated. The dependences for the PDS and light intensity in the defect layer on the parameters characterizing absorption and gain are obtained. We investigated the possibility of connections between the PDS and the density of the light energy accumulated in the system. The influence of the defect layer and CLC layer on the PDS are investigated. It is shown that the PDS is maximum when the defect is in the centre of the system. We showed also that the subject system can work as a low threshold laser, a multiposition trigger, filter, etc.

physics.optics↗
arXiv2017

Permanent Magnets Undulator for Terahertz FEL

The terahertz FEL ferromagnetic undulator has been created. The length of the undulator period is 9cm, number of the periods is 27. By means of selection and redistribution of magnetic elements the spread of amplitudes of the magnetic field was reduced to 7%. Additional windings of magnetic elements were used to compensate for residual spread. Required focusing gradient of magnetic field was obtained as a result of relative displacement of alternating poles with opposite charge of magnetic field along the x axis. Parameters of undulator including focusing properties in the horizontal plane were investigated.

physics.acc-ph↗
arXiv2017

Cholesteric liquid crystals with tunable defect inside

Peculiarities of the defect modes of cholesteric liquid crystals (CLCs) with an isotropic/anisotropic defect inside are investigated. The influence of the defect layer thickness and its anisotropy of refraction, the influence of the system thickness and of the defect layer position in the system, as well as the influence of the dielectric borders on the defect modes is investigated. It is shown that it is possible to change reflection at the defect modes in wide intervals and change the defect mode wavelength, by tuning the defect location and its thickness. Such a system possesses transmission asymmetry. Also, the CLC system thickness and the refraction coefficient of the medium bordering the CLC layer on its both sides have essential influence on the reflection at the defect mode and on the reflection frequency.

physics.optics↗
arXiv2017

Composite Cell from Nematic and Cholesteric Liquid Crystals as an Rotator of Electrically Tunable Polarization Plane

A liquid crystal optical device made of an optically anisotropic heterostructure is considered. The device consists of a cholesteric liquid crystal (CLC) layer sandwiched by two phase-shifting anisotropic layers of a nematic liquid crystal (NLC). In this structure each of the NLC layers is a quarterwave plate. The problem is solved both by Ambartsumian method of layer addition and Muller matrix method. The peculiarities of reflection spectra, eigen polarizations, rotation of polarization plane and polarization ellipticity are studied. It is shown that this device can work as a light modulator or a system for obtaining linearly polarized light with electrically tunable rotation of the polarization plane (which is especially important for optical communication), as well as a device for obtaining the linearly polarized light from a non-polarized one.

physics.optics↗
arXiv2004

Controlling a group velocity of light by magnetic field

We have shown that quantum interference in a driven quasi-degenerate two-level atomic system can be controlled by an externally applied magnetic field. We demonstrate that the mechanism of optical control is based on quantum interference, which allows one to implement both electromagnetically induced transparency and electromagnetically induced absorption in one atomic system. Dispersion of such the medium allows one to control group velocity of propagation of light pulses be ultra-slow or superluminal via applied magnetic field.

quant-ph↗
arXiv2002

Free-Electron Lasers Without Inversion: Design of Two-Magnet Drift Region

We propose a two-magnet design of a drift region for a free-electron laser without inversion (FELWI). By performing direct calculations of the phase shifts for electrons passing the drift region, we prove that the small-signal gain integrated over the detuning is positive and is inversely proportional to the energy spread of the ``hot'' electron beam. The dispersion and the geometry of the drift region are specified, and the requirements to the electron beam quality, including the transverse size and the angular spread, are found.

physics.optics↗
arXiv1994

Quantum Group Random Walks in Strongly Correlated $2+1$ $D$ Spin Systems

We consider the temporal evolution of strong correlated degrees of freedom in $2+1$~$D$ spin systems using the Wilson operator eigenvalues as variables. It is shown that the quantum-group diffusion equation at deformation parameter $q$ being the $k$-th root of unity has the polynomial solution of degree $k$.

cond-mat↗