arXiv subjects

D. V. Karlovets

Publications and source records attributed to D. V. Karlovets.

At least 19 recordsLinked to original sources

arXiv2026

Generation of high-OAM ultraviolet twisted light for RF-photoinjector applications

The generation of relativistic vortex electron beams via photoemission requires ultraviolet laser beams with well-controlled orbital angular momentum (OAM) and compatibility with radio-frequency (RF) photoinjector drive-laser systems. High-OAM vortex beams at a wavelength of 266 nm are generated using three fabricated diffractive optical elements integrated into an operational photoinjector beamline: a reflective fork grating, a high-topological-charge spiral phase plate, and binary axicons. The spiral phase plate produces a high-purity Laguerre-Gaussian mode with an OAM of l = 64 and a conversion efficiency of 80%, whereas binary axicons generate low-divergence quasi-Bessel beams forming a superposition of multiple OAM states with a finite OAM bandwidth imposed by their binary phase structure. Fork gratings provide flexible access to lower OAM values and enable robust modal diagnostics. The generated beams are characterized using cylindrical-lens mode conversion and radial intensity analysis, demonstrating practical control of both the OAM content and spectral bandwidth of ultraviolet structured light for accelerator-based applications.

quant-ph↗

arXiv2026

Radiation of breathing vortex electron packets in magnetic field

When a vortex electron with an orbital angular momentum (OAM) enters a magnetic field, its quantum state is described with a nonstationary Laguerre-Gaussian (NSLG) state rather than with a stationary Landau state. A key feature of these NSLG states is oscillations of the electron wave packet's root-mean-square (r.m.s.) radius, similar to betatron oscillations. Classically, such an oscillating charge distribution is expected to emit photons. This raises a critical question: does this radiation carry away OAM, leading to a loss of the electron's vorticity? To investigate this, we solve Maxwell's equations using the charge and current densities derived from an electron in the NSLG state. We calculate the total radiated power and the angular momentum of the emitted field, quantifying the rate at which a vortex electron loses its energy and OAM while propagating in a longitudinal magnetic field. We find both the radiated power and the angular momentum losses to be negligible indicating that linear accelerators (linacs) appear to be a prominent tool for maintaining vorticity of relativistic vortex electrons and other charged particles, at least in the quasi-classical approximation.

quant-ph↗

arXiv2026

Photon emission by vortex particles accelerated in a linac

We study the photon emission by charged spinless particles with phase vortices and an orbital angular momentum (OAM) projection in longitudinal electric and magnetic fields within the scalar QED. A realistic wave packet of an electron or ion accelerated by a radio-frequency wave locally feels a constant and spatially homogeneous field, which allows us to develop an effective model for losing the angular momentum of the vortex particle due to photon emission. For the fields typical for accelerator facilities, we find that an effective lifetime of the vortex state greatly exceeds the acceleration time. This proves that the acceleration of vortex electrons, ions, muons, and so forth to relativistic energies is possible in conventional linacs, as well as in the wake-field accelerators with higher field gradients, the OAM losses due to the photon emission are mostly negligible, and that the vortex quantum state is highly robust against these losses.

hep-ph↗

arXiv2026

Classical and quantum beam dynamics simulation of the RF photoinjector test bench

We present beam-dynamics simulations for an S-band RF photoinjector test bench under development at the Joint Institute for Nuclear Research, aimed at producing high-quality electron beams and enabling future generation of relativistic vortex electrons with a quantized orbital angular momentum (OAM). Simulations of the 1.5-cell photogun are performed assuming an RF gradient of 45 MV/m, which, in accordance with our simulations with CST Studio, corresponds to the currently achieved input RF power of 3 MW. At low charge (Q = 0.63 pC), stable bunch formation is obtained, with weak space-charge effects and transverse emittance dominated by RF-induced correlations. Optimization of the injection phase and cathode solenoid results in a robust emittance-compensated regime with a final normalized emittance of 2.08 pi mm mrad. To assess prospects for accelerating vortex electron beams, we additionally model the quantum evolution of single-electron Laguerre-Gaussian wave packets. The results show that multi-MeV acceleration suppresses free-space spreading of the electron packet and preserves the packet's initial OAM structure, indicating that the test bench provides suitable conditions for forthcoming experimental studies of relativistic vortex electrons.

physics.acc-ph↗

arXiv2025

Phase-space description of photon emission

Interactions between charged particles and light occur in real space and time, yet quantum field theory usually describes them in momentum space. Whereas this approach is well suited for calculating emission probabilities and cross sections, it is insensitive to spatial and temporal phenomena such as, for instance, radiation formation, quantum coherence, and wave packet spreading. These effects are becoming increasingly important for experiments involving electrons, photons, atoms, and ions, particularly with the advent of attosecond spectroscopy and metrology. Here, we propose a general method for describing the emission of photons in phase space via a Wigner function. Several effects for Cherenkov radiation are predicted, absent in classical realm or in quantum theory in momentum space, such as a finite spreading time of the photon, finite duration of the flash and a quantum shift of the photon arrival time. The photon spreading time turns out to be negative near the Cherenkov angle, the flash duration is defined by the electron packet size, and the temporal shift can be both positive and negative. The characteristic time scales of these effects lie in the atto- and femtosecond ranges, thereby illustrating atomic origins of these macroscopic phenomena. The near-field distribution of the photon field resembles the electron packet shape, thus making ``snapshots'' of the emitter wave function. Our approach can easily be generalized to the other types of radiation and extended to scattering, decay, and annihilation processes, bringing tomographic methods of quantum optics to particle physics.

quant-ph↗

arXiv2025

Generation of Deep Ultraviolet Optical Vortices via Amplitude and Phase Spiral Zone Plates

We present the development and experimental implementation of diffractive optical elements designed to generate optical vortices in the deep ultraviolet range (from 260 to 266 nm). These elements, fabricated using advanced lithographic and etching techniques, facilitate the efficient transformation of Gaussian beams into twisted modes carrying orbital angular momentum. Experimental tests conducted using the laser driver of an RF photoinjector at JINR successfully demonstrate the generation of deep-ultraviolet optical vortices with a topological charge of l = 1. These findings underscore the potential of structured light in the deep ultraviolet range for applications in relativistic electron beam studies and beam manipulation technologies.

physics.optics↗

arXiv2025

Generating entangled pairs of vortex photons via induced emission

Pairs of entangled vortex photons can promise new prospects of application in quantum computing and cryptography. We investigate the possibility of generating such states via two-level atom emission induced by a single photon wave packet with a definite total angular momentum (TAM). The entangled pair produced in this process possesses well-defined mean TAM with the TAM variation being much smaller than $\hbar$. On top of that, the variation exponentially decreases with the increase in TAM of the incident photon. Our model allows one to track the time evolution of the state of the entangled pair. An experimentally feasible scenario is assumed, in which the incident photon interacts with a spatially confined atomic target. We conclude that induced emission can be used as a source of entangled vortex photons with applications in atomic physics experiments, quantum optics, and quantum information sciences.

quant-ph↗

arXiv2025

Nonstationary Laguerre-Gaussian states in magnetic field

The Landau states of electrons with orbital angular momentum in magnetic fields are important in the quantum theories of metals and of synchrotron radiation at storage rings, in relativistic astrophysics of neutron stars, and in many other areas. In realistic scenarios, electrons are often born inside the field or injected from a field-free region, requiring nonstationary quantum states to account for boundary or initial conditions. This study presents nonstationary Laguerre-Gaussian (NSLG) states in a longitudinal magnetic field, characterizing vortex electrons after their transfer from vacuum to the field. Comparisons with Landau states and calculations of observables such as mean energy and r.m.s. radius show that the r.m.s. radius of the electron packet in the NSLG state oscillates in time around a significantly larger value than that of the Landau state. This quantum effect of oscillations is due to boundary conditions and can potentially be observed in various problems, particularly when using magnetic lenses of electron microscopes and linear accelerators. Analogies are drawn between a quantum wave packet and a classical beam of many particles in phase space, including the calculation of mean emittance of the NSLG state as a measure of their quantum nature.

quant-ph↗

arXiv2024

Generation of vortex electrons by atomic photoionization

We explore the process of orbital angular momentum (OAM) transfer from a twisted light beam to an electron in atomic ionization within the first Born approximation. The characteristics of the ejected electron are studied regardless of the detection scheme. We find that the outgoing electron possesses a definite projection of OAM when a single atom is located on the propagation axis of the photon, whereas the size of the electron wave packet is determined solely by the energy of the photon rather than by its transverse coherence length. Shifting the position of the atom yields a finite dispersion of the electron OAM. We also study a more experimentally feasible scenario - a localized finite-sized atomic target - and develop representative approaches to describing coherent and incoherent regimes of photoionization.

physics.atom-ph↗

arXiv2024

Absorption of a twisted photon by an electron in strong magnetic field

The work investigates absorption of a twisted photon, which possesses quantized total angular momentum (TAM), by a relativistic electron with the Lorentz factor $γ\sim 1-10$ in a strong magnetic field up to the Schwinger limit, $H_c = 4.4\cdot 10^{13}$ G. We examine the absorption cross sections and their dependence on the parameters of the incident photon and the initial Landau electron. It is found that total absorption cross sections decrease as angular momentum of the incident photon increases and increase as angular momentum of the initial electron grows. The process is also compared across different magnetic field strengths, and the contribution of various electron spin transitions to total absorption cross section is analyzed. We also find that the processes without an electron spin flip dominate and, on top of that, an asymmetry in the ``spin-down'' $\rightarrow$ ``spin-up'' and the ``spin-up'' $\rightarrow$ ``spin-down'' transitions is observed. Specifically, the cross sections for the ``spin-down'' $\rightarrow$ ``spin-up'' transition are larger, which can be interpreted as an analogy of the Sokolov-Ternov effect present for photon emission. Finally, the cross sections are found to be almost constant as the transverse momentum of the photon varies from $0.1$ eV to $100$ keV. Our findings can help to improve the understanding of the QED processes in critical fields, typical for astrophysical environments, e.g. magnetospheres of neutron stars.

hep-ph↗

arXiv2024

Studying highly relativistic vortex-electron beams by atomic scattering

We explore the opportunities of using electron scattering by screened Coulomb potential as a tool to retrieve properties of the relativistic vortex beams of electrons, such as their transverse momentum and orbital angular momentum (OAM). We focus on relativistic and ultra-relativistic regimes of the electron energies of at least several MeV and higher, in which the transverse beam momentum is typically much smaller than its longitudinal momentum. Different scattering scenarios for the incident electron beam are considered. In particular, the scattering by a very wide target can be used to probe the electron transverse momentum when its values are larger than 10 keV. The scattering by a target of a width comparable to that of the incident beam allows one to obtain information about the electron OAM. Varying target sizes in the range from couple to hundreds of nanometers, one can in principle distinguish OAM values from several units of $\hbar$ up to thousands and more.

physics.atom-ph↗

arXiv2024

Detecting Hollow Electron Beams via Smith-Purcell Radiation from a Metasurface

Hollow electron beams are today highly desirable for many applications, but are still challenging in view of their detection. In this Letter, we focus on the unique character of the electromagnetic radiation that relativistic hollow electron beams can produce when traveling above a metasurface. We investigate theoretically the specific features of the radiation in a coherent mode, which provides the highest intensity, and show that the radiation from a hollow beam can be considerably more intense than that from a conventional solid beam. This solves the problem of distinguishing between hollow and solid beams. Moreover, we consider the two-layer internal structure of a hollow beam and reveal that the radiation characteristics are sensitive to the width and population of each layer. This allows detecting the internal structure of hollow beams. Interestingly, we found that the factor describing the annular beam form is a separated multiplier in a conventional form factor, independent of the properties of periodic structure. Thus, we can conclude that our results will stay correct for different profiles of periodic structures and metasurfaces made of metaatoms of different topologies and forms. The results pave the way towards a variety of newly emerging applications based on hollow electron beams, very diverse in topics, such as manipulation of objects at the nano-level, studies of chiral matter, plasma acceleration in donut wakefields and even applications in huge facilities such as LHC for controlling proton beam halos etc.

physics.optics↗

arXiv2024

Transmission of vortex electrons through a solenoid

We argue that it is generally nonstationary Laguerre-Gaussian states (NSLG) rather than the Landau ones that appropriately describe electrons with orbital angular momentum both in their dynamics at a hard-edge boundary between a solenoid and vacuum and inside the magnetic field. It is shown that the r.m.s. radius of the NSLG state oscillates in time and its period-averaged value can significantly exceed the r.m.s. radius of the Landau state, even far from the boundary. We propose to study the unconventional features of quantum dynamics inside a solenoid in several experimental scenarios with vortex electrons described by the NSLG states. Relevance for processes in scanning and transmission electron microscopes, as well as for particle accelerators with relativistic beams is emphasized.

quant-ph↗

arXiv2023

Vavilov-Cherenkov emission with a twist: a study of the final entangled state

We present a theoretical investigation of the Vavilov-Cherenkov (VC) radiation by a plane-wave or twisted electron. Special emphasis is put on the question whether and at what conditions the emitted VC photons can be twisted. For this aim we obtain a general expression in the coordinate and momentum representations for the quantum state of the final electron-photon system that is a result of the radiation process itself and does not depend on the properties of a detector. It is shown that this evolved state is an entangled state of an electron and a photon, and both particles can be twisted. A direct consequence of this result follows: if one uses a detector sensitive to the twisted electron (photon) with the definite projection of the total angular momentum (TAM), then the final photon (electron) also will be in the twisted state with a definite TAM projection. Further, we investigate the polarization properties of the final twisted photon in more general conditions than has been calculated before. Finally, we exploit a close similarity between the discussed VC radiation and the process of the equivalent photon emission in the Weizsäcker-Williams method and find the corresponding final state.

quant-ph↗

arXiv2023

Shifting physics of vortex particles to higher energies via quantum entanglement

Physics of structured waves is currently limited to relatively small particle energies as the available generation techniques are only applicable to the soft $X$-ray twisted photons, to the beams of electron microscopes, to cold neutrons, or non-relativistic atoms. The highly energetic vortex particles with an orbital angular momentum would come in handy for a number of experiments in atomic physics, nuclear, hadronic, and accelerator physics, and to generate them one needs to develop alternative methods, applicable for ultrarelativistic energies and for composite particles. Here, we show that the vortex states of in principle arbitrary particles can be generated during photon emission in helical undulators, via Cherenkov radiation, in collisions of charged particles with intense laser beams, in such scattering or annihilation processes as $eμ\to eμ, ep \to ep, e^-e^+ \to p\bar{p}$, and so forth. The key element in obtaining them is the postselection protocol due to entanglement between a pair of final particles and it is largely not the process itself. The state of a final particle -- be it a $γ$-ray, a hadron, a nucleus, or an ion -- becomes twisted if the azimuthal angle of the other particle momentum is measured with a large error or is not measured at all. As a result, requirements to the beam transverse coherence can be greatly relaxed, which enables the generation of highly energetic vortex beams at accelerators and synchrotron radiation facilities, thus making them a new tool for hadronic and spin studies.

hep-ph↗

arXiv2022

Generation of vortex particles via generalized measurements

The hard X-ray twisted photons and relativistic massive particles with orbital angular momentum -- vortex electrons, muons, protons, etc. -- have many potential applications in high-energy and nuclear physics. However, such states can be obtained so far mainly via diffraction techniques, not applicable for relativistic energies. Here we show that the vortex states of different particles, including hadrons, ions, and nuclei, can be generated in a large class of processes with two final particles simply by altering a postselection protocol. Thanks to entanglement and to the uncertainty relations, an evolved state of a final particle becomes twisted if the momentum azimuthal angle of the other particle is measured with a large uncertainty. We give several examples, including Cherenkov and undulator radiation, particle collisions with intense laser beams, $eμ\to eμ, ep \to ep$. This technique can be adapted for ultrarelativistic lepton and hadron beams of linear colliders, and it can also facilitate the development of sources of X-ray and $γ$-range twisted photons at storage rings and free-electron lasers.

hep-ph↗

arXiv2022

Evolution of the accelerated charged vortex particle in an inhomogeneous magnetic lens

We present a detailed analysis of the capture and acceleration of a non-relativistic charged vortex particle (electron, positron, proton, etc.) with an orbital angular momentum in a field of an axisymmetric electromagnetic lens, typical for a linear accelerator. We account for the acceleration as well as for the inhomogeneity of both electric and magnetic fields that may arise from some real-life imperfections. We establish conditions when the wave packet can be captured and successfully transported through the lens. We describe the transition process and explain how a free Laguerre-Gaussian packet could be captured into the Landau state of the lens preserving its structure for all moments in time. Several representative examples are provided to illustrate developed formalism.

quant-ph↗

arXiv2021

Reply to Comment on "Nonlinear quantum effects in electromagnetic radiation of a vortex electron" by A. Karnieli, R. Remez, I. Kaminer, et al

We argue that while the experiment of Remez et al. is interesting and its conclusions may well be correct, the observed lack of dependence of the measured distributions on the electron's transverse coherence length should have been expected for the parameters chosen. This is because for Smith-Purcell radiation it is the coherence length of a virtual photon that plays a role of the radiation formation width and not the entire electron's coherence length that can well be orders of magnitude larger. This is a common feature for all the radiation processes in which a photon is emitted not directly by the electron, which can be delocalized in space, but rather by a much better localized atom or a conduction electron on a surface. Therefore, in our opinion the results of Remez et al. cannot rule out the alternative hypothesis of the delocalized charge. The question, mainly addressed in the comment by Karnieli et al., of whether the measurements were performed in the wave zone or not is interesting but secondary. We emphasize that the measured distributions are unusually wide and neither the original paper nor the recent comment fully discusses and rules out all alternative hypotheses that could have led to the same distributions. On the contrary, there exists a family of classical effects that could also have resulted in the measured distributions and that were neither discussed nor even mentioned by the authors. Such alternative hypotheses include (i) effects of the beam sizes, of its angular divergence, of the temporal coherence of the process, and (ii) influence of the grating shape and of its material. Finally, we propose to repeat the experiment and to measure diffraction radiation from a thin metallic semi-plane or Compton emission in a laser pulse. In these cases, the classical effects play a much smaller role and the results of such measurements would have higher credibility.

quant-ph↗