Structured relativistic electron and neutron vortex beams in intense laser fields

CFEL Theory Seminar

  • Datum: 20.04.2016
  • Uhrzeit: 14:00 - 15:00
  • Vortragende(r): Armen Hayrapetyan
  • Max-Planck-Institut für Physik Komplexer Systeme, Dresden
  • Ort: CFEL (Bldg. 99)
  • Raum: Seminar Room IV, O1.111
  • Gastgeber: Nina Rohringer
Recent advances in technology and instrumentation have made it possible to generate vortex beams of electrons and neutrons with phase singularities at their cores, where the beam intensity is zero and the phase is undefined. These new types of beams, apart from the spin angular momentum, carry a quantized orbital angular momentum (OAM) along their axes of propagation resulting in a twisted wavefronts, pretty much like quantum tornadoes. The OAM of electron is capable of fundamentally altering the physics of beams and is already being used for application purposes in electron microscopy.

In this talk, I will discuss how the spin and OAM degrees of freedom give rise to an intrinsic spin-orbit coupling (also called spin-to-orbit conversion) in structured relativistic quantum waves. The main focus of my talk will be on the interaction of such twisted, both charged and neutral, matter waves with intense laser pulses. In order to demonstrate the possibility of controlling of vortex beams both in the transverse direction and in the temporal domain, we develop an exact relativistic quantum theory by constructing two new sets of solutions to generalized Dirac equations, accounting for the interaction of electrons and neutrons with external electromagnetic fields. In more details, using the fundamental superposition principle of (linear) relativistic quantum electrodynamics, we superimpose a multitude of plane-wave charged (Volkov) or neutral (Skobelev) states over a mono-energetic cone representing a twisted Bessel state. We show that the laser field gives rise to a Lorentz-induced shift of the vortex core of twisted electrons, the transverse profile of which maintains its overall shape throughout the propagation in a pulse. In contrast, while the vortex core of twisted neutrons remains unaffected, the spin- and OAM-dependent profile experiences an inhomogeneous distribution due to the interaction of neutron's anomalous magnetic moment with the magnetic field of the laser.

Our new, Bessel-type solutions may be employed in many fields of physics, from atomic and subatomic physics to topological condensed matter theory, and can be useful for evaluating matrix elements for various laser-assisted scattering processes, especially, at high intensities.

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