Measurement of structured tightly focused beams with classical interferometry

We report the first classic interferometric measurement of the full field of propagating tightly focused vector beams (NA up to 1.23) across areas of similar to 3 lambda x 3 lambda - 7 lambda x 7 lambda. This approach outperforms near field measurements of non paraxial propagating beams because it is compatible with large power imbalances across the polarization components and low light intensities. Also, intricate subwavelength structures are resolved due to the exact mapping of the transverse field components by the microscope. Prior to focusing, the structured laser light has a linear or circular polarization state and an arbitrary 2D spatial phase. The transverse polarization components are extracted directly from 12 interferograms using 4 step interferometry, while the longitudinal component is extracted from the measured transverse fields with Gauss law. Different structured propagating vectorial beams are measured to demonstrate that the method works for any field geometry. The measurements are compared to simulations with normalized cross correlations that yield mean values ? 0.8, confirming good agreement.