Converting Evanescent Waves into Propagating Waves: The Super-Resolution Mechanism in Microsphere-Assisted Microscopy

The lateral resolution beyond the classical diffraction limit can be achieved by the combination of a dielectric microsphere and an optical microscope, and this paper utilizes microsphere-assisted microscopy as a platform to study the mechanism of using optical microstructure to realize super-resolution imaging. A barium titanate glass (BTG) microsphere was immersed into ethanol, and the imaging resolution of a BTG microsphere-assisted microscope was recorded in situ during evaporation of ethanol, while a numerical simulation was done to study how the ethanol’s immersion depth affected the BTG microsphere’s capability to convert evanescent waves in the near field to propagating waves in the far field. The experimental trend of the imaging resolution versus the immersion depth was consistent with that of the conversion capability. Our results indicate that super-resolution may come from the conversion of evanescent waves into propagating waves by the optical microstructure.