Microsphere-assisted microscopy: Contribution to the understanding of label-free super-resolution (Conference Presentation)

The demands of biological imaging microscopy continue to progress, requiring high spatial resolution, real time acquisition, easy-to-use devices and with preference being label-free to avoid cell damage. While recent advances have allowed significant progress in resolution, several limitations remain such as the use of labelling, the complexity of the imaging technique or low image rate acquisition. Recently, a new optical technique, known as microsphere-assisted microscopy, seems to provide several advantages. The principle is based on the collection of a virtual image of the sample through a dielectric microsphere by a classical optical microscope. The dielectric microsphere with a diameter of tens of micrometres, can be deposited on the sample in air or in immersion. A resolution of up to 7 times smaller than the wavelength has been experimentally demonstrated in full-field imaging, i.e. without the need for point scanning nor labelling, with a classical optical microscope. Our team has also demonstrated that beyond a classical image the phase can also be measured using this technique with an interferometric configuration, so providing depth information. The presentation will be focused on the physical understanding of the phenomenon through simulations. The role of the photonic jet, light coherence and near-field effects have been numerically investigated. We will show how the photonic jet can be used to explain the imaging process but does not explain the super-resolution phenomenon. The role of coherence in the resolution limit criterion will also be illustrated, as well as a discussion on the contribution of the evanescent wave.