Measurement of structured tightly focused vector beams with classical interferometry

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.