Novel techniques of optical detection and observation of periodic crystals
Desai, Darshan Bhadresh
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The aim of this dissertation is to demonstrate non-interferometric far-field observation and detection of two-dimensional periodic crystals with truly high lateral resolution at visible frequencies using some of the contemporary techniques. The Plasmonic and Non-plasmonic Ultra-Thin optical condensers based on illumination of object using evanescent surface waves that can be resonantly coupled to propagating waves for imaging with enhanced resolution in the far-field region are discussed. Also, simple and efficient optical condensers formed in wet-mounting setups that can be easily reconfigured for obtaining variable condenser numerical aperture are shown to provide enhanced lateral resolution for optical detection of two-dimensional periodic crystals that are nearly eight times smaller than the Rayleigh resolution limit, and then, using a series of experiments and computations simulations, the origin of mysterious condenser-like behavior in such setups is discussed. Although it is always possible to tweak the experimental setup for obtaining enhanced lateral resolution, combining numerical processing techniques with experimental process of image acquisition permits even better performance. Optical observation of periodic crystals using phase-retrieval imaging technique called Fourier Ptychographic Microscopy is demonstrated using Hemispherical Digital Condensers. It is demonstrated that for imaging two-dimensional periodic crystals with single spatial periodicity, the resolution limit of Fourier Ptychographic Microscopy is the Rayleigh resolution limit. The source of this limitation on the resolution is demonstrated to have been identified using experiments and computational simulations, and then, a recently proposed technique of imaging two-dimensional periodic crystals called Dual-Space Microscopy that was presented to overcome this limitation is demonstrated to achieve super-resolution imaging of two-dimensional periodic crystals.