Measurement of structured tightly focused vector beams with classical interferometry

TL;DR

This paper presents a novel interferometric method for fully measuring the electric field of tightly focused vector beams, including all components, with high accuracy and applicability to various beam geometries.

Contribution

It introduces the first approximation-free measurement technique for the complete field of tightly focused vector beams, including longitudinal components, using 12 interferograms and Gauss law.

Findings

High correlation (≥0.8) between measurements and simulations

Method works for any structured beam geometry

Verified spin-orbit coupling in vortex beams

Abstract

We report the first measurement with no approximations of the full field of tightly focused vector beams (NA up to $1.23$) across areas of $\sim 9-49\,\lambda ^2$. Prior to focusing, the structured laser light has a linear or circular polarization state. The transverse components are extracted directly from 12 interferograms using 4 step interferometry, while the longitudinal component is extracted from the transverse fields with Gauss law. Different structured beams are measured to demonstrate that the method works for any field geometry. In the case of circular polarization we use vortex beams to verify the appearance of spin-orbit coupling in the axial component. The measurements are compared with simulations with normalized cross correlations that yield mean values $\geq 0.8$, confirming good agreement.