Localization and migration of phase singularities in the edge-diffracted optical-vortex beams

TL;DR

This paper investigates how optical vortex cores move and deform during diffraction at a sharp edge, revealing complex trajectories and structures that depend on beam type and diffraction conditions, with implications for optical metrology.

Contribution

It provides a detailed analysis of the complex trajectories of phase singularities in diffracted optical vortex beams, supported by simulations, analytical models, and experiments, highlighting their sensitivity to diffraction parameters.

Findings

Optical vortex cores follow spiral-like trajectories during edge diffraction.

Trajectory structures vary with beam type, showing loops and self-crossings in Kummer beams.

Trajectories are highly sensitive to diffraction conditions, useful for metrological applications.

Abstract

When a circularly-symmetric light beam with optical vortex (OV) diffracts at an opaque screen with the sharp edge, the OV core is displaced from the beam axis and, in case of the m-charged incident OV, decomposed into |m| single-charged ones. By means of numerical simulations and based on examples of incident beams with topological charges |m| =1, 2, 3 we show that, while the screen edge monotonously advances towards the beam axis, the OVs in the diffracted beam cross section move away from the incident beam axis along spiral-like trajectories. The trajectories contain fine structure details that reflect the nature and peculiar spatial configuration of the diffracting beam. For the Kummer beams' diffraction, the trajectories contain self-crossings and regions of "backward" rotation (loops); in case of Laguerre-Gaussian beams, the trajectories are smoother. The numerical results are supported by analytical approximations and conform with experiment The general shape of the trajectories and their local behavior show high sensitivity to the diffraction conditions (spatial structure of the diffracting beam, its disposition with respect to the screen edge, etc.), which can be used in diverse metrological applications.