Abstract
Electron vortex beams offer unique opportunities for the study of chiral or magnetic structures in electron microscopes and of fundamental effects of quantum interference in particle physics. Immersing a cathode in a solenoid field presents a highly efficient and flexible method for the generation of vortex electron beams which is utilized at accelerators, but has not yet been realized in an electron microscope. The conditions for the generation of vortex beams with quantized orbital angular momentum from an immersed cathode in an electron microscope are discussed, and general possibilities of this technique for the production of vortex beams of other charged particles are pointed out.
Highlights
The generation of vortex beams as twisted photons [1], vortex neutrons [2], or vortex electrons has inspired versatile theoretical studies and interesting experiments or proposals to unveil the basic properties of such beams and of effects of quantum interference and coherence in particle collisions, inaccessible with ordinary beams [3,4,5,6,7,8,9]
Quantized vortex electrons—i.e., electron beams carrying a quantized orbital angular momentum (OAM)—generated in electron microscopes [10,11,12] can be applied as probes for the study of chiral [13] or magnetic structures [14] and enable magnetic mapping with atomic resolution [15]
The prevailing technique for the generation of vortex electron beams applied in accelerators makes use of a cathode which is immersed in a solenoid field
Summary
The generation of vortex beams as twisted photons [1], vortex neutrons [2], or vortex electrons has inspired versatile theoretical studies and interesting experiments or proposals to unveil the basic properties of such beams and of effects of quantum interference and coherence in particle collisions, inaccessible with ordinary beams [3,4,5,6,7,8,9]. The prevailing technique for the generation of vortex electron beams applied in accelerators makes use of a cathode which is immersed in a solenoid field This immersion of the cathode changes the dynamics of charged particle beams in a very fundamental way. The beams created with the use of an immersed cathode carry typically a large average angular momentum with a broad spectral distribution, or OAM bandwidth This technique can be adapted to the generation of vortex beams of all kinds of charged particles. While applications in a microscope do not necessarily require the generation of pure modes with a well-defined angular momentum and a vanishing OAM quantum uncertainty (OAM bandwidth), the discussion concentrates on this operation mode to point out the most stringent requirements General possibilities of this technique for the production of vortex beams of other charged particles are highlighted
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