arXiv subjects

A. Y. Bekshaev

Publications and source records attributed to A. Y. Bekshaev.

5 recordsLinked to original sources

arXiv2026

Controllable localization and manipulation of optical hollow traps by means of optical-vortex diffraction

An optical vortex (OV) is coupled with the local intensity zero and is thus a field configuration suitable for "hollow" optical traps and optical tweezers. When an incident circular OV beam experiences diffraction at a rectilinear screen edge (SE), and the conditions of weak diffraction perturbation (the SE is far enough from the beam axis) are fulfilled, the main consequence is the OV-core displacement from its initial (axial) position. Based on the model of incident Laguerre-Gaussian (LG) beam, we investigate analytically and numerically the ways of controlling the OV-core position in the diffracted-field cross section by means of changing the SE position with respect to the incident-beam axis. The results show that regulating the SE position with ~1 mcm accuracy (which is available for existing mechanical tools), controllable OV-core motion with a sub-nanometer accuracy can be realized. Possible modifications of this motion depending on the incident beam topological charge, wavefront curvature, SE properties (semitransparent screen, phase-step screen) and the distance between the diffraction plane and the observation plane are analyzed. The conditions most favorable for the micro-object trapping and manipulation are specified and discussed.

physics.optics↗

arXiv2022

Non-extensive thermodynamics of the radiation in heterogeneous thermal plasmas

Thermodynamic characteristics of the radiation of condensed combustion products presented in the form of agglomerates of metal-oxide nanoparticles demonstrate deviations from the classical Planck's law. We propose to interpret these deviations in terms of the non-additive entropy of the photon system interacting with the heterogeneous combustion products, which makes it possible to use the non-extensive Tsallis thermodynamics for their description. It is assumed that the non-additive character of the radiation entropy in heterogeneous plasma can be explained by the influence of long-range interactions and non-equilibrium physicochemical processes. An expression is obtained for the energy-dependent distribution of the photon density, based on the phenomenological parameter of non-extensiveness $q$ which, in the first approximation, does not depend on the energy. In this case, the "non-extensive" Planck's law can be reduced to the "usual" Planck distribution by introducing the "effective temperature" that exceeds the real temperature. Numerical modelling has shown that the spectral density of photons, the position and magnitude of its maximum depend on the value of the parameter $q$, which can be used for its experimental determination and revelation of its physical nature and origin.

physics.plasm-ph↗

arXiv2021

Energy and momentum of the surface plasmon-polariton supported by a thin metal film

We study the energy and momentum of the surface plasmon-polariton (SPP) excited in a symmetric 3-layer "insulator-metal-insulator" structure, which is known to support the symmetric (S) mode with the negative group velocity as well as the antisymmetric (AS) mode with only positive energy flow. The electric and magnetic field vectors are calculated via both the phenomenological and the microscopic approach; the latter involves the hydrodynamic model accounting for the quantum statistical effects for the electron gas in metal. Explicit representation for the energy and momentum constituents in the dielectric and in the metal film are obtained, and the wavenumber dependences of the energy and momentum contributions for the whole SPP are analyzed numerically. The various energy and momentum constituents are classified with respect to their origin: "field" or "material", and the physical nature: orbital (canonical) and spin (Belinfante) momentum contributions. The pictures characteristic for the S and AS modes are systematically compared. The results can be useful for the studies and applications of the SPP-induced thin-film effects, in particular, for the charge and spin dynamics in thin-film plasmonic systems.

physics.optics↗

arXiv2018

Electric current induced unidirectional propagation of surface plasmon-polaritons

Nonreciprocity and one-way propagation of optical signals is crucial for modern nanophotonic technology, and is typically achieved using magneto-optical effects requiring large magnetic biases. Here we suggest a fundamentally novel approach to achieve unidirectional propagation of surface plasmon-polaritons (SPPs) at metal-dielectric interfaces. We employ a direct electric current in metals, which produces a Doppler frequency shift of SPPs due to the uniform drift of electrons. This tilts the SPP dispersion, enabling one-way propagation, as well as zero and negative group velocities. The results are demonstrated for planar interfaces and cylindrical nanowire waveguides.

physics.optics↗

arXiv2016

Direct measurements of the extraordinary optical momentum and transverse spin-dependent force using a nano-cantilever

Known since Kepler's observation that a comet's tail is oriented away from the sun, radiation pressure stimulated remarkable discoveries in electromagnetism, quantum physics and relativity [1,2]. This phenomenon plays a crucial role in a variety of systems, from atomic [3-5] to astronomical [6] scales. The pressure of light is associated with the momentum of photons, and it is usually assumed that both the optical momentum and the radiation-pressure force are naturally aligned with the propagation of light, i.e., its wavevector. Here we report the direct observation of an extraordinary optical momentum and force directed perpendicular to the wavevector, and proportional to the optical spin (i.e., degree of circular polarization). Such optical force was recently predicted for evanescent waves [7] and other structured fields [8]. It can be associated with the enigmatic "spin-momentum" part of the Poynting vector, which was introduced by Belinfante in field theory 75 years ago [9-11]. We measure this unusual transverse momentum using a nano-cantilever capable of femto-Newton resolution, which is immersed in an evanescent optical field above the total-internal-reflecting glass surface. Furthermore, the transverse force we measure exhibits another polarization-dependent contribution determined by the imaginary part of the complex Poynting vector. By revealing new types of optical forces in structured fields, our experimental findings revisit fundamental momentum properties of light and bring a new twist to optomechanics.

physics.optics↗