Characterization of highly focused vector fields using phase retrieval: a practical guide

Experimentally measuring the longitudinal component of a highly focused electromagnetic field is challenging, especially when using near-field technology methods. We recently demonstrated that this component can be estimated by combining optical and numerical techniques. This method involves determining the complex amplitude of the transverse field in the focal region using phase retrieval techniques. Subsequently, the field is numerically propagated, and the longitudinal component is estimated using Gauss's theorem. This Application Note discusses the experimental details and potential sources of error that could affect the results. Additionally, we introduce a graphical application that streamlines the process and helps in selecting appropriate parameters to achieve satisfactory outcomes.