Rapid characterization of metasurface unit cells using Scanning Differential Heterodyne Microscopy

The performance of metasurfaces is reduced due to factors like fabrication uncertainties and near-field coupling, which can be solved by direct characterization of individual elements. Recent techniques use near-field scanning to observe direct properties of elements, which use AFM tips that are not stable for large areas. In this study, we demonstrate Scanning Differential Heterodyne Microscopy (SDHM) technique as a tool for phase and amplitude characterization of unit cells in reflective phase-gradient metasurfaces with the aim to predict the far-field performance. The use of heterodyne 2-probe beam scanning to monitor surface modulations, provides fundamental advantage of rapid and robust phase-amplitude optical data acquisition essential for large scale metasurface investigations and applications.