The Electromagnetic Properties Of Vortex Electron Beam And Its Interaction With Atoms

The wave function of a convention electron beam is a plane wave.However,in2007,a vortex electron beam was theoretically proposed,and the experiment confirmed it in 2010.The vortex electron beam possesses a singular phase and quantized orbital angular momentum which make it different from the plane wave electron beam.Electron beam has widely applications in radiation physics,material detection and fundamental research.Therefore,when a new electron beam-vortex electron beam-appeared,it soon attracted attention in these fields.A potentially important application is using two vortex electron beams with opposite topological charges to detect the magnetic material by the chiral dependence electron magnetic circular dichroism(chiral-EMCD).This kind of detection can obtain nanometer or even atomic scale spatial resolution.However,its physical mechanism is still unclear.Early research focused on the nonrelativistic vortex electron beam.Recently,researches of the relativistic vortex electron beam and relativistic vortex electron wavepacket are emerging.The electromagnetic fields and radiation properties of the relativistic vortex electrons yet investigated.In response to these problems,this thesis studied the electromagnetic properties of relativistic vortex electron beam and the radiation properties of relativistic vortex electron wavepacket,and explored the physical mechanism of chiral-EMCD,and achieved the following results:First,we propose a new mechanism of generate chiral-EMCD.In experiment,the energy loss spectrum of electron beam passing through a material is used to detect the material structure.The vortex electron beam with hundreds ke V energy passes through the material with energy loss above 100 e V,which causes the transition of the core electrons of the material,and the collective effect of free electrons can be ignored,so that the interaction between vortex electron beam and material can be attributed to the interaction between vortex electron and atom.Previous researches(Phys.Rev.Lett.108,074802 and Phys.Rev.A,86,023816)on the interaction between vortex electron beam and atom have shown that chiral-EMCD is difficult to produce.In this thesis,we propose to study the interaction of vortex electron beam and atom in an uniform magnetic field.The conservation of angular momentum keep the magnetic quantum numbers of the scattering channels excited by two vortex electron beams with opposite topological charges are opposite.If spin-orbit coupling is not considered,there is no chiral-EMCD,and if Zeeman effect isn't considered,there is no chiral-EMCD too.With joint effect of the Zeeman effect and spin orbit coupling,the joint occupation probability amplitude of atomic initial-final states for two symmetric scattering channels with opposite magnetic quantum numbers are unequal,which makes the two transition channels have different transition probabilities,and generates chiral-EMCD.The new mechanism of chiral-EMCD proposed in this paper is expected to provide theoretical guidance for the chiral detection of magnetic material and promote the application of vortex electron beam in material detection.Second,we have studied the electromagnetic fields and its properties of a relativistic vortex electron beam.We calculated the electromagnetic field of a relativistic vortex electron beam,and found that the electromagnetic field contains two parts,one part corresponds to the electromagnetic field of a nonrelativistic vortex electron beam,and the other part dependent on the spin-orbit coupling is the intrinsic property of the relativistic vortex electron beam.Therefore,it is further proposed that the difference of electromagnetic fields between the relativistic vortex electron beams with spin-up and spin-down can be used to detect the spin-orbit coupling effect.Third,we find a radiation mechanism of electromagnetic radiation due to the relativistic vortex electron wavepacket dispersion.Unlike the wave function of a vortex electron beam which has an infinite spatial distribution,a relativistic vortex electron wavepacket has a local spatial distribution.The relativistic vortex electron wavepacket is superposed by a series of base modes(such as plane wave or Bessel beam).During the wave propagation,the wavepacket dispersion cause the time-dependent interference between the different base modes,and further to make the time-dependent charge density and current density which cause the radiation field.These charge and current densities can be decomposed into a steady state part and a harmonic part,the static fields are induced by the steady part,while the harmonic part generated radiation fields.The multipole analysis of the radiation field in far feld shows a magnetic-dipole radiation.We have calculated the radiation field numerically and found that its intensity is proportional to the topological charge and depends on the spin states of vortex beam.The dispersive radiation proposed in this paper is a new radiation mechanism,which is different from the two basic radiation mechanisms(Bremsstrahlung due to the acceleration of electron and polarized radiation due to electrons uniformly move in a media).