Image Formation by Contact Microspheres from First Principles: Mechanism and Resolution

ABSTRACT Contact dielectric microspheres have emerged as super‐lenses boosting significantly optical resolution, but there is a controversy in this field regarding the mechanism of super‐resolution and an apparent mismatch between the experimental resolution claims of around and theoretical predictions of around . To address this, here the imaging of a finite grating with period comparable to the Abbe limit of is investigated using an ab initio modeling that includes key imaging steps: object illumination, wave scattering, and image formation. It is shown that unlike the standard lenses, which only transform the waves scattered by the object, microspheres can also provide additional coherent illumination of the object by the circulating waves. Their scattering gives rise to new diffraction orders, enabling the imaging of features that would be otherwise unresolved. The visibility of sub‐wavelength features can also be greatly enhanced by removing small‐angle illumination. The resolution of the ab initio images is estimated by a comparison with that in the incoherent model of imaging and by Fourier analysis, giving reasonable agreement with experimental results in the literature. Simple formulas for the resolution by adopting the Abbe theory to microspherical imaging are proposed.