Measuring the orbital angular momentum spectrum of an electron beam

Abstract

Electron waves that carry orbital angular momentum (OAM) are characterized by a quantized and unbounded magnetic dipole moment parallel to their propagation direction. When interacting with magnetic materials, the wavefunctions of such electrons are inherently modified. Such variations therefore motivate the need to analyse electron wavefunctions, especially their wavefronts, to obtain information regarding the material's structure. Here, we propose, design and demonstrate the performance of a device based on nanoscale holograms for measuring an electron's OAM components by spatially separating them. We sort pure and superposed OAM states of electrons with OAM values of between −10 and 10. We employ the device to analyse the OAM spectrum of electrons that have been affected by a micron-scale magnetic dipole, thus establishing that our sorter can be an instrument for nanoscale magnetic spectroscopy.

Design of electrostatic phase elements for sorting the orbital angular momentum of electrons

“…It is therefore necessary to have efficient phase elements that can be used to manipulate the electron wavefunction. One approach involves the introduction of phase holograms that are made from nanofabricated SiN films of varying thickness [11,20]. However, such an approach results in a reduction in efficiency and does not allow the phase to be tuned dynamically.…”

Ultrafast generation and control of an electron vortex beam via chiral plasmonic near fields

“…In the opposite limit, when the transverse extension of the wave function significantly exceeds the scale of the internal features of the proton, the influence of the internal charge density quickly averages out, thereby yielding a magnetic moment equal to ℓ typical of a point-like particle with nuclear magneton . Several schemes could be used to measure such a quantity, including a Stern-Gerlach-like approach (41) or devices that couple the OAM of a charged particle with its spin (42,43). The latter would be extremely valuable for probing the proton internal spin dynamics by means of OAM impartment, thus potentially unraveling the role played by the OAM of its inner constituents in the determination of its total spin.…”

“…Vortices in electron waves have also become increasingly present in modern science, especially in electron microscopy (11)(12)(13)(14). Combining the OAM of the vortex beam with the charge of the electrons results in an increased sensitivity to local magnetic properties (15,16). Both optical and electron beams that carry OAM can be produced by means of passive devices that directly modify their wave structure, such as spiral phase plates (17), along with amplitude (18) and phase holograms (19,20).…”

Twisted Surface Plasmons with Spin‐Controlled Gold Surfaces

“…Since discovery in 1990s, it is believed that the optical OAM beam can be utilized as an auxiliary dimension to further increase the capacity of information for various important applications, such as optical data storage and communications in both classical and quantum optical regime . Besides optical systems, the OAM properties have also been investigated in electronics and acoustics, inspiring various revolutionary developments and potential applications like acoustic OAM multiplexed communication, electron OAM spectrometer, etc. The eigenstates of elementary particles with different topological charges are orthogonal to each other, making it possible to individually produce, evaluate, screen, and manipulate the OAMs of different orders with on‐chip devices, which would be of interest and significant value for emerging OAM‐based nanotechnologies.…”