Label-free super-resolution optical microscopy

Abstract

To see structures well below 200 nm using visible light, super-resolution techniques have been developed. Most of these techniques rely on fluorescence labelling or use of artificial materials to go beyond the Abbe limit. Therefore, achieving super-resolution in the label-free regime is the problem that is being addressed in this thesis. In this work, high-index contrast dielectric waveguides are employed for microscopy. Typically, wide waveguides are employed for bio-imaging applications. High-index contrast wide waveguides support multiple optical modes to guide optical power along its length. Therefore, the first task was to use multiple modes to artificially induce intensity fluctuations that are compatible with fluorescence based super-resolution algorithms. This enabled the generation of super-resolved fluorescence images. The next task was to see if these multiple-modes can be used to illuminate unlabeled samples. By averaging several images within the integration time of the camera, a high-contrast label-free image was generated using these waveguides. Finally, to achieve super-resolution in label-free mode, photoluminescence in Si3N4 waveguides was used for near-field illumination of unlabeled samples. This helped realize a label-free incoherent imaging system, thus permitting the application of fluorescence-based super-resolution algorithms to achieve super-resolution in label-free mode.