arXiv subjects

Tomasz Radożycki

Publications and source records attributed to Tomasz Radożycki.

10 recordsLinked to original sources

arXiv2026

Polarization-controlled optical backflow in paraxial electromagnetic beams

Optical backflow in paraxial Gaussian beams is investigated within the Maxwell framework. Scalar potential representations are employed to identify conditions under which the longitudinal Poynting component becomes negative, showing that backflow is enabled by local suppression of the leading-order transverse field and the dominance of higher-order vectorial contributions. The spatial topology of backflow regions is shown to be governed by polarization through the number of independent local constraints on the transverse field. When the local polarization phase is free, as in the generic case of circular polarization, the leading-order field vanishes only at isolated points, giving rise to point-like backflow regions (extended curves may arise if an additional global phase constraint is imposed). In contrast, when the polarization phase is locally fixed, as for linear, radial, or azimuthal polarization, the suppression condition reduces to a single real constraint, resulting in extended backflow curves. Analytical Gaussian-polynomial solutions explicitly illustrate these effects. These results clarify the role of vectorial interference, establish a polarization-controlled backflow geometry, and provide a foundation for further studies of optical backflow in structured and nonparaxial beam configurations, as well as potential applications in optical manipulation and structured light design.

physics.optics↗

arXiv2026

Spin-induced and orbital quantum backflow in Pauli theory

We show that quantum backflow in spin-$\tfrac{1}{2}$ systems within the Pauli framework can arise from spin-dependent contributions to the probability current. We construct explicit two-mode states in which the orbital current reduces to a uniform drift, so that no interference between longitudinal momentum components is present in this sector. In such configurations, backflow is generated entirely by spinor structure, which induces time-dependent modulations of the local current leading to flux reversal, while the longitudinal momentum distribution remains strictly supported on positive momenta. We derive analytical conditions for backflow in terms of spinor and momentum parameters, allowing direct control of the effect via internal degrees of freedom. We further analyze spatial coarse-graining, showing exponential suppression of interference and a qualitatively different scaling of orbital and spin contributions, with spin-induced backflow remaining robust in regimes where orbital effects are strongly suppressed.

cond-mat.mes-hall↗

arXiv2026

Two mechanisms of backward optical forces on Rayleigh particles in structured paraxial light

A theoretical and numerical study of optical forces acting on a Rayleigh particle in a paraxial Gaussian light beam exhibiting regions of optical backflow is presented. Within the dipole approximation, the total optical force is decomposed into gradient, scattering, and spin-curl terms. Vector fields satisfying the exact paraxial Maxwell equations are employed to describe the structured light configuration responsible for two distinct mechanisms leading to backward optical forces. The first originates from the local reversal of the Poynting vector, which induces a negative longitudinal momentum flux, while the second arises from the spin-dependent component of the force associated with the spatial variation of the optical spin density. Analytical expressions and numerical simulations confirm that both mechanisms can produce backward motion of a Rayleigh particle under appropriate beam conditions. These results provide a unified physical picture of backward-directed optical forces in Gaussian beams and open possibilities for particle manipulation in structured light fields.

physics.optics↗

arXiv2025

Backflow in vector Gaussian beams

The phenomenon of Poynting backflow in a single vector Gaussian beam is examined. The paraxial Maxwell equations and their exact solutions containing terms proportional to the small parameter $\varepsilon=\fracλ{2πw_0}$, or to its square, where $w_0$ is the beam waist, are made use of. Explicit analytical calculations show that just these additional expressions are responsible for the occurrence of the reversed Poynting-vector longitudinal component for selected polarizations. Concrete results for the time-averaged vector for several Gaussian beams with $n=1$ ($n$ being the topological index of the beam) are presented. Depending on the choice of polarization, the backflow area is located around the beam's axis, has an annular character or is absent. In the case of $n=2$, backflow areas were found as well. The magnitude of the backflow proved to be proportional to $\varepsilon^4$.

physics.optics↗

arXiv2023

Paraxial Dirac equation

In this work, the paraxial approximation of the free Dirac equation is examined. The results are first obtained by constructing superpositions of exact solutions with suitable profiles, which are borrowed from paraxial optics. In this manner, the paraxial Dirac beams are obtained in four cases: as Gaussian, Bessel-Gaussian, modified Bessel-Gaussian and elegant Laguerre-Gaussian beams. In the second part of the work, the paraxial Dirac equation is derived, and then its solutions in the aforementioned cases are directly obtained. All the resulting wave functions conform to those derived formerly by virtue of superpositions, except for terms, that are negligible upon the assumption that the paraxial functions along the propagation axis vary only slightly over a distance equal to the de Broglie wavelength, which is the standard paraxial requirement.

physics.class-ph↗

arXiv2023

Properties of "special'' hyperbolic Bessel-Gaussian optical beams

An explicit formula for a new type of beams, which in this work are called the "special" hyperbolic Bessel-Gaussian (SHBG) beams, has been derived, using the method of the Hankel transform formulated in our previous work. The fundamental properties of these beams are analyzed. The parameters that define the beam shape have been identified and related to those of the fundamental Gaussian beam. The analytical expressions for the SHBG beams include an additional parameter $γ$, which allows the beam's shape to be modified to some extent. In the plane perpendicular to the propagation direction, these beams exhibit the annular nature. Interestingly, initially (i.e. near the beam's spot) a single ring splits into a number of rings as one is moving along the beam. This is especially apparent for $γ$ close to unity, as this effect then appears for values of $z$ relatively small compared to the Rayleigh length i.e., where the energy concentration in the beam is still high. The phase of the wave, whose behavior is in certain aspects typical of modes having the vortex character, is also studied in this paper.

physics.optics↗

arXiv2023

Constructing various paraxial beams out of regular and modified Bessel-Gaussian modes

Various superpositions of Bessel-Gaussian beams and modified Bessel Gaussian beams are considered. Two selected parameters characterizing these beams, with respect to which the superpositions are constructed, are the topological index $n$ associated with the orbital angular momentum carried by the beam, and $χ$ related to the dilation of the beam. It is shown that, from these modes, by choosing appropriate weighting factors, it is possible to create a number of well- and less-known solutions of the paraxial equation: Gaussian (shifted and non-shifted) beam, $γ$ beam, Kummer-Gaussian beam, special hyperbolic Bessel-Gaussian beam, a certain special Laguerre-Gaussian beam, and generalized paraxial beams in hyperbolic and regular versions.

physics.optics↗

arXiv2021

A concise and universal method for deriving arbitrary paraxial and non-paraxial cylindrical Gaussian-type light modes

A concise method of deriving expressions for Gaussian-like solutions of the paraxial and d'Alembert equations is presented. This method is based on the Hankel transform. Choosing some Gaussian base functions with slight modifications of the prefactor all basic beams of cylindrical character can be easily obtained. This refers to Gaussian, Bessel-Gaussian, modified Bessel-Gaussian, Laguerre-Gaussian and Kummer-Gaussian (i.e., Hypergeometric-Gaussian) beams although potentially other beams can come into play as well. For instance a new type of a beam that can be derived in this way is described through the incomplete gamma function so it may be called a $γ$ beam.

physics.optics↗

arXiv2018

Guiding neutral particles endowed with a magnetic moment by an electromagnetic wave carrying orbital angular momentum. II. Quantum mechanics

The quantum mechanical states of the neutral particle endowed with a magnetic moment in the combination of electromagnetic vortex field together with the constant magnetic field are dealt with. It is shown that this system of fields is capable to capture the particle in the perpendicular direction and guide it along the propagating wave. The quantum evolution is subject to tunneling processes, which can destroy the delicate trapping mechanism. The probability of these processes show that it should be in principle possible to catch and guide the particle for the time of several microseconds. This time can be lengthened by the appropriate adjustments of the external magnetic field.

quant-ph↗

arXiv2016

Trapping neutral particles endowed with a magnetic moment by an electromagnetic wave carrying orbital angular momentum: Semiclassical theory

The motion of a neutral atom endowed with a magnetic moment interacting with the magnetic field is determined from the Ehrenfest-like equations of motion. These equations for the average values of the translational and spin degrees of freedom are derived from the Schrödinger-Pauli wave equation and they form a set of nine coupled nonlinear evolution equations. The numerical and analytic solutions of these equations are obtained for the combination of the rotating magnetic field of a wave carrying orbital angular momentum and a static magnetic field. The running wave traps the atom only in the transverse direction while the standing wave traps the atom also in the direction of the beam.

physics.atom-ph↗