Label-Free Nanoscopy with Contact Microlenses: Super-Resolution Mechanisms and Limitations

TL;DR

This paper investigates how contact microlenses can surpass the diffraction limit in super-resolution imaging by analyzing the physical mechanisms, especially optical coupling effects, using modeling and experiments.

Contribution

It provides a detailed analysis of the super-resolution mechanisms with contact microlenses, emphasizing the role of coherent coupling effects and artifacts in imaging.

Findings

Coherent imaging introduces artefacts and zero-intensity points.

Out-of-phase oscillations can produce images with virtually unlimited resolution.

Experimental results confirm the formation of arbitrary shapes due to nanoplasmonic coupling.

Abstract

Despite all the success with developing super-resolution imaging techniques, the Abbe limit poses a severe fundamental restriction on the resolution of far-field imaging systems based on diffraction of light. Imaging with contact microlenses, such as microspheres or microfibers, can increase the resolution by a factor of two beyond the Abbe limit. The theoretical mechanisms of these methods are debated in the literature. In this work, we focus on the recently expressed idea that optical coupling between closely spaced nanoscale objects can lead to the formation of the modes that drastically impact the imaging properties. These coupling effects emerge in nanoplasmonic or nanocavity clusters, photonic molecules, or various arrays under resonant excitation conditions. The coherent nature of imaging processes is key to understanding their physical mechanisms. We used a cluster of point dipoles, as a simple model system, to study and compare the consequences of coherent and incoherent imaging. Using finite difference time domain modeling, we show that the coherent images are full of artefacts. The out-of-phase oscillations produce zero-intensity points that can be observed with practically unlimited resolution (determined by the noise). We showed that depending on the phase distribution, the nanoplasmonic cluster can appear with the arbitrary shape, and such images were obtained experimentally.