Investigation of far-field super-resolution imaging by microsphere-based optical microscopy

Optical microscopy techniques have recently been shown to have the capability to exceed the diffraction limit when a microsphere is used. The mechanism involved in super-resolution imaging is theoretically analysed in this paper. A microsphere is also known to generate a photonic nanojet with a waist smaller than the diffraction limit. This nanojet is used as near-field illumination, and interacts with the sample to give a passive spatial frequency shift for the sample, meaning that near-field evanescent waves containing high-frequency spatial information about the sample can be converted into far-field propagating waves. This method is simple and cost-effective, and offers a promising approach for achieving far-field super-resolution imaging. Our theoretical analysis of super-resolution imaging is verified based on numerical and experimental results.