Measuring the non-separability of spatially disjoint vectorial fields

TL;DR

This paper introduces a novel measure for quantifying the non-separability of spatially disjoint vectorial light fields, addressing a gap in existing tools for analyzing complex structured light with varying local polarisation homogeneity.

Contribution

The authors develop and experimentally validate a new measure that accurately captures local path-like separability in vectorial light fields with spatially varying polarisation structures.

Findings

The measure correctly accounts for local disjointness in scalar components.

Experimental results demonstrate the measure's effectiveness in complex light fields.

Addresses a key gap in quantifying non-separability in structured light.

Abstract

Vectorial forms of structured light that are non-separable in their spatial and polarisation degrees of freedom have become topical of late, with an extensive toolkit for their creation and control. In contrast, the toolkit for quantifying their non-separability, the inhomogeneity of the polarisation structure, is far less developed, and in some cases fails altogether. To overcome this, here we introduce a new measure for vectorial light, which we demonstrate both theoretically and experimentally. We consider the general case where the local polarisation homogeneity can vary spatially across the field, from scalar to vector, a condition that can arise naturally if the composite scalar fields are path separable during propagation, leading to spatially disjoint vectorial light. We show how the new measure correctly accounts for the local path-like separability of the individual scalar beams, which can have varying degrees of disjointness, even though the global vectorial field remains intact. Our work attempts to address a pressing issue in the analysis of such complex light fields, and raises important questions on spatial coherence in the context of vectorially polarised light.