Twisted Electron Research Articles

Holographic Generation of Highly Twisted Electron Beams

Free electrons can possess an intrinsic orbital angular momentum, similar to those in an electron cloud, upon free-space propagation. The wave front corresponding to the electron’s wave function forms a helical structure with a number of twists given by the angular speed. Beams with a high number of twists are of particular interest because they carry a high magnetic moment about the propagation axis. Among several different techniques, electron holography seems to be a promising approach to shape a conventional electron beam into a helical form with large values of angular momentum. Here, we propose and manufacture a nanofabricated phase hologram for generating a beam of this kind with an orbital angular momentum up to 200ℏ. Based on a novel technique thevalue of orbital angular momentum of the generated beam is measured and then compared with simulations. Our work, apart from the technological achievements, may lead to a way of generating electron beams with a high quanta of magnetic moment along the propagation direction and, thus, may be used in the study of the magnetic properties of materials and for manipulating nanoparticles.

Scattering of twisted relativistic electrons by atoms

The Mott scattering of high-energetic twisted electrons by atoms is investigated within the framework of the first Born approximation and Dirac's relativistic equation. Special emphasis is placed on the angular distribution and longitudinal polarization of the scattered electrons. In order to evaluate these angular and polarization properties we consider two experimental setups in which the twisted electron beam collides with either a single well-localized atom or macroscopic atomic target. Detailed relativistic calculations have been performed for both setups and for the electrons with kinetic energy from 10 to 1000 keV. The results of these calculations indicate that the emission pattern and polarization of outgoing electrons differ significantly from the scattering of plane-wave electrons and can be very sensitive to the parameters of the incident twisted beam. In particular, it is shown that the angular- and polarization-sensitive Mott measurements may reveal valuable information about both the transverse and longitudinal components of the linear momentum and the projection of the total angular momentum of twisted electron states. Thus, the Mott scattering emerges as a diagnostic tool for the relativistic vortex beams.

Holographic generation of highly twisted electron beams.

Free electrons can possess an intrinsic orbital angular momentum, similar to those in an electron cloud, upon free-space propagation. The wave front corresponding to the electron's wave function forms a helical structure with a number of twists given by the angular speed. Beams with a high number of twists are of particular interest because they carry a high magnetic moment about the propagation axis. Among several different techniques, electron holography seems to be a promising approach to shape a conventional electron beam into a helical form with large values of angular momentum. Here, we propose and manufacture a nanofabricated phase hologram for generating a beam of this kind with an orbital angular momentum up to 200ℏ. Based on a novel technique the value of orbital angular momentum of the generated beam is measured and then compared with simulations. Our work, apart from the technological achievements, may lead to a way of generating electron beams with a high quanta of magnetic moment along the propagation direction and, thus, may be used in the study of the magnetic properties of materials and for manipulating nanoparticles.

Structured x-ray beams from twisted electrons by inverse Compton scattering of laser light

The inverse Compton scattering of laser light on high-energetic twisted electrons is investigated with the aim to construct spatially structured x-ray beams. In particular, we analyze how the properties of the twisted electrons, such as the topological charge and aperture angle of the electron Bessel beam, affects the energy and angular distribution of scattered x-rays. We show that with suitably chosen initial twisted electron states one can synthesize tailor-made x-ray beam profiles with a well-defined spatial structure, in a way not possible with ordinary plane-wave electron beams.

Radiative capture of twisted electrons by bare ions

Recent advances in the production of twisted electron beams with a subnanometer spot size offer unique opportunities to explore the role of orbital angular momentum in basic atomic processes. In the present work, we address one of these processes: radiative recombination of twisted electrons with bare ions. On the basis of the density matrix formalism and the non-relativistic Schrödinger theory, analytical expressions are derived for the angular distribution and the linear polarization of photons emitted due to the capture of twisted electrons into the ground state of (hydrogen-like) ions. We show that these angular and polarization distributions are sensitive to both the transverse momentum and the topological charge of the electron beam. To observe in particular the value of this charge, we propose an experiment that makes use of the coherent superposition of two twisted beams.

Electron with orbital angular momentum in a strong laser wave

Electrons carrying orbital angular momentum (OAM) have recently been discovered theoretically and obtained experimentally that opens up possibilities for using them in high-energy physics. We consider such a twisted electron moving in external field of a plane electromagnetic wave and study how this field influences the electron's OAM. Being motivated by the development of high-power lasers, we focus our attention on a classically strong field regime for which $-e^2 \bar {A^2}/m_e^2 c^4 \gtrsim 1$. It is shown that along with the well-known "plane-wave" Volkov solution, Dirac equation also has the "non-plane-wave" solutions, which possess OAM and a spin-orbit coupling, and generalize the free-electron's Bessel states. Motion of the electron with OAM in a circularly polarized laser wave reveals a twofold character: the wave-packet center moves along a classical helical trajectory with some quantum transverse broadening (due to OAM) existing even for a free electron. Using the twisted states, we calculate the electron's total angular momentum and predict its shift in the strong-field regime that is analogous to the well-known shifts of the electron's momentum and mass (and to a less known shift of its spin) in intense fields. Since the electron's effective angular momentum is conserved in a plane wave, as well as in some more general field configurations, we discuss several possibilities for accelerating non-relativistic twisted electrons by using the focused and combined electromagnetic fields.

Is the [9]Annulene Cation a Möbius Annulene?

Does it do the twist? High-level theoretical calculations show that the [9]annulene cation exists in two isomers: a twisted 4n electron Mobius aromatic compound, and a non-twisted boat-like Huckel conformation (see scheme). The latter form was detected by laser flash photolysis experiments; an example of a stable, charged, or uncharged parent Mobius annulene is still elusive.

Twisted intra-molecular electron transfer phenomenon of dansyl immobilized on chitosan film and its sensing property to the composition of ethanol–water mixtures

A new fluorescent chitosan film bearing dansyl as a fluorophore has been prepared. The film shows dual fluorescence phenomenon due to twisted intra-molecular charge transfer (TICT) in the excited state of the fluorophore. The position of the maximum emission of the film depends on the polarity of the medium, and it shifts from 460 nm in ethanol to 505 nm in water. The two emissions have been attributed to the emission from the “locally excited” state or non-charge transfer excited state of dansyl and that from the TICT excited state of the fluorophore, respectively. Existence of TICT phenomenon of the immobilized dansyl has been confirmed and studied by various fluorescence techniques, such as fluorescence lifetime measurement, steady-state and time-resolved fluorescence emission spectroscopy measurements, etc. The ratio, I505/I460, of the intensities of the two emission bands depends linearly on the concentration of water in ethanol–water mixture provided the concentration is less than 40%. Furthermore, the sensing property of the film to the mixture is reversible.