Programming Metasurface Near‐Fields for Nano‐Optical Sensing

Control of optical fields at the nanoscale holds the promise of fast, efficient imaging methods, but is elusive due to the diffraction limit. This paper investigates how a single metasurface patch in the near field of a sample plane may be used to create a wide variety of intensity patterns by applying different illumination profiles from the far field. Numerical analysis shows that one metasurface patch may be used to generate complete bases of illumination patterns on a grid as fine as lambda/16. The limits of control are explored in terms of degrees of freedom on the illumination side and spatial resolution on the sample side. These illumination patterns are expected to enable sub-wavelength structured illumination microscopies, compressive imaging and sensing. Quantitative analysis of how the engineered fields may be used for detection of small scattering particles demonstrates the potential the approach holds for nanoscale optical sensing.