Polarization radiation of vortex electrons with large orbital angular momentum

Abstract

Vortex electrons, -freely propagating electrons whose wavefunction has helical wavefronts, -could become a novel tool in the physics of electromagnetic radiation. They carry a non-zero intrinsic orbital angular momentum (OAM) with respect to the propagation axis and, for 1, a large OAM-induced magnetic moment, µ ≈ µB (µB is the Bohr magneton), which influences the radiation of electromagnetic waves. Here, we consider in detail the OAM-induced effects by such electrons in two forms of polarization radiation, namely in Cherenkov radiation and transition radiation. Thanks to the large , we can neglect quantum or spin-induced effects, which are of the order of ω/Ee 1, but retain the magnetic moment contribution ω/Ee 1, which makes the quasiclassical approach to polarization radiation applicable. We discuss the magnetic moment contribution to polarization radiation, which has never been experimentally observed, and study how its visibility depends on the kinematical parameters and the medium permittivity. In particular, it is shown that this contribution can, in principle, be detected in azimuthally non-symmetrical problems, for example when vortex electrons obliquely cross a metallic screen (transition radiation) or move nearby it (diffraction radiation). We predict a left-right angular asymmetry of the transition radiation (in the plane where the charge radiation distributions would stay symmetric), which appears due to an effective interference between the charge radiation field and the magnetic moment one. Numerical values of this asymmetry for vortex electrons with Ee = 300 keV and = O(100 − 1000) are O(0.1 − 1%), and we argue that this effect could be detected with existing technology. The finite conductivity of the target and frequency dispersion play the crucial roles in these predictions.

Scattering of wave packets with phases

“…They were shown to be solutions of the wave equations [7][8][9][10][11][12][13][14], and the corresponding beams of photons, electrons, and neutrons were generated in recent years [15][16][17][18][19][20]. Vortex electrons with the kinetic energy of 200 − 300 keV can be focused to a spot of anÅngström size [21], their OAM can be as high as = 200 [22], their magnetic moment increases proportionally to [13], and this brings about new effects in the electromagnetic radiation [23,24]. Such photons and electrons were also proved useful for optical manipulation [14], for probing phase of a transition amplitude, for creating pairs entangled in their OAM [25][26][27][28][29][30], etc.…”

“…where 24) and the Heaviside function is extended so that Θ(0) = 1. This Wigner function can be negative, it is invariant under the Lorentz boosts along the z axis, and it coincides up to a common factor with the so-called Wolf function in optics (see eq.…”

Quantum calculation of the Vavilov-Cherenkov radiation by twisted electrons

“…[12], vortex electron beams were experimentally demonstrated [13,14] and a number of remarkable effects they produce was investigated [15]. Electromagnetic radiation of vortex electrons has not yet been investigated experimentally, but theoretical works suggest that it should display interesting effects in transition radiation [16,17] and Vavilov-Cherenkov radiation [10].…”

Holographic Generation of Highly Twisted Electron Beams

“…In the latter case, the magnetic moment of EVBs, in addition to spin-1 2 of the electron is coupled into internal dy- In this Letter, we report the generation of twisted EBs with an OAM value of 200 -the highest electron OAM quanta up to now. Achieving an EB with high number of twists provides the possibility of exploring the transition between the quantum and classical regime of electromagnetic radiations inside a medium, where the spin-induced effects are diminished [18]. This transition is particularly interesting in view of observing phenomena such as polarization radiation, which has never been experimentally observed.…”

“…Achieving an EB with high number of twists provides the possibility of exploring the transition between the quantum and classical regime of electromagnetic radiations inside a medium, where the spin-induced effects are diminished [18]. This transition is particularly interesting in view of observing phenomena such as polarization radiation, which has never been experimentally observed.…”