Optical-vortex diagnostics via Fraunhofer slit diffraction with controllable wavefront curvature

TL;DR

This paper introduces a method to determine both the magnitude and sign of optical vortex topological charge by analyzing asymmetries in far-field slit diffraction patterns influenced by wavefront curvature.

Contribution

It demonstrates that incorporating the incident beam's spherical wavefront allows for simultaneous measurement of topological charge magnitude and sign in optical vortices.

Findings

Far-field diffraction asymmetry depends on wavefront curvature and TC sign.

Method enables quick, reliable OV diagnostics.

Applicable to OV-based metrology and information processing.

Abstract

Far-field slit-diffraction of circular optical-vortex (OV) beams is efficient for measurement of the topological charge (TC) magnitude but does not reveal its sign. We show that this is because in the common diffraction schemes the diffraction plane coincides with the incident OV waist plane. With explicit involvement of the incident beam spherical wavefront and based on the examples of Laguerre-Gaussian modes we show that the far-field profile possesses an asymmetry depending on the wavefront curvature and the TC sign. These features enable simple and efficient ways for the simultaneous diagnostics of the TC magnitude and sign, which can be useful in many OV applications, including the OV-assisted metrology and information processing.