Extension of Friedel's law to Vortex Beam Diffraction

TL;DR

This paper extends Friedel's law to vortex beams, showing that diffraction patterns of vortex beams with opposite topological charges are centrosymmetric, regardless of the scattering object’s symmetry, supported by simulations and experiments.

Contribution

It introduces a generalized Friedel's law for vortex beams, revealing a new symmetry property in their diffraction patterns.

Findings

Diffraction patterns of vortex beams with opposite charges are centrosymmetric.

The extended law holds regardless of the scattering object's symmetry.

Numerical and experimental data verify the theoretical extension.

Abstract

Friedel's law states that the modulus of the Fourier transform of real functions is centrosymmetric, while the phase is antisymmetric. As a consequence of this, elastic scattering of plane wave photons or electrons within the first-order Born-approximation as well as Fraunhofer diffraction on any aperture, is bound to result in centrosymmetric diffraction patterns. Friedel's law, however, does not apply for vortex beams, and centrosymmetry in general is not present in their diffraction patterns. In this work we extend Friedel's law for vortex beams by showing that the diffraction patterns of vortex beams with opposite topological charge, scattered on the same two dimensional potential, always are centrosymmetric to one another, regardless of the symmetry of the scattering object. We verify our statement by means of numerical simulations and experimental data. Our research provides deeper understanding in vortex beam diffraction and can be used to design new experiments to measure the topological charge of vortex beams with diffraction gratings, or study general vortex beam diffraction.