Resolution and Reciprocity in Microspherical Nanoscopy: Point-Spread Function Versus Photonic Nanojets

Super-resolution imaging through contact microspherical lenses is often linked to the ability of dielectric microspheres to form photonic nanojets, and to the reciprocity of focusing and imaging. By rigorously solving Maxwell's equations, the authors show that this common understanding of the origin of super-resolution is not valid. Furthermore, they apply the concept of the point-spread function in combination with magnification of the virtual image to provide a basis for quantifying the resolution in wide-field microspherical nanoscopy. These results are expected to strongly influence near-field imaging beyond the diffraction limit.