A unified formulation of dichroic signals using the Borrmann effect and twisted photon beams
Abstract
Dichroic signals derived from the Borrmann effect and a twisted photon beam with topological charge l = 1 are formulated with an effective wavevector. The unification applies for non-magnetic and magnetic materials. Electronic degrees of freedom associated with an ion are encapsulated in multipoles previously used to interpret conventional dichroism and Bragg diffraction enhanced by an atomic resonance. A dichroic signal exploiting the Borrmann effect with a linearly polarized beam presents charge-like multipoles that include a hexadecapole. A difference between dichroic signals obtained with a twisted beam carrying spin polarization (circular polarization) and opposite winding numbers presents charge-like atomic multipoles, whereas a twisted beam carrying linear polarization alone presents magnetic (time-odd) multipoles. Charge-like multipoles include a quadrupole, and magnetic multipoles include a dipole and an octupole. We discuss the practicalities and relative merits of spectroscopy exploiting the two remarkably closely-related processes.
Keywords
Cite
@article{arxiv.1801.06012,
title = {A unified formulation of dichroic signals using the Borrmann effect and twisted photon beams},
author = {Stephen P Collins and Stephen W Lovesey},
journal= {arXiv preprint arXiv:1801.06012},
year = {2018}
}