Igor P. Ivanov, Dmitry V. Karlovets
Electromagnetic radiation can be emitted not only by particles' charges but also by magnetic moments and higher electric and magnetic multipoles. However experimental proofs of this fundamental fact are extremely scarce. In particular, the magnetic moment contribution has never been observed in any form of polarization radiation. Here, we propose to detect it using vortex electrons carrying large orbital angular momentum (OAM) $\ell$. The relative contribution of the OAM-induced magnetic moment, $\ell \hbar \omega/E_e$, becomes much larger than the spin-induced contribution $\hbar \omega/E_e$, and it can be observed experimentally. As a particular example, we consider transition radiation from vortex electrons obliquely indicent on a boundary between vacuum and a dispersive medium, in which the magnetic moment contribution manifests itself via angular asymmetry. For electrons with $E_e = 300$ keV and $\ell = 100-1000$ we predict asymmetry of order 0.1%-1%, which could be measurable with existing technology. Thus, vortex electrons emerge as a new tool in the physics of electromagnetic radiation.
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http://arxiv.org/abs/1304.0359
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