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Surface Plasmon Assisted High Resolution and High Contrast Optical Imaging

Abstract

This thesis presents theoretical and/or experimental demonstrations of several Surface Plasmon (SP) assisted high-resolution or high-contrast microscopy techniques, including Plasmonic Structured Illumination Microscopy (PSIM), Plasmonic Darkfield (PDF) Microscopy, Plasmonic Evanescent field (PEF) Microscopy and Localized Surface Plasmon Assisted Contrast (LSPAC) Microscopy. The PSIM combines tunable SP interference with structured illumination microscopy (SIM) to achieve super-resolution. By replacing the laser interference fringes in conventional SIM with SP interference (SPI) patterns, PSIM possesses higher image resolving power compared to that of SIM. Both theoretical and experimental concept demonstration shows more than 2.6-fold resolution improvement compared with conventional epi-fluorescence microscopy, whereas SIM only achieves about 2 times resolution improvement. This new PSIM technique is a wide field super resolution imaging technique and potentially could be used for high speed biomedical imaging. The PDF microscopy is a compact, alignment-free dark-field microscopy technique. Experimental results show that it is capable of forming dark-field images of the specimens by utilizing a highly integrated chip-scale plasmonic condenser. The PEF microscopy is a similar technique that exploits the extremely short z decay length of high wave vector SP waves for achieving selective excitation of fluorophores very close to the substrate. Both the PDF and PEF microscopy possess high z resolution and high imaging contrast and are suitable for the dynamics study near the contact regions of living cells and the substrate. The LSPAC microscopy combines localized surface plasmon resonance (LSPR) and dark field microscopy technique for high contrast purpose. Because of the sensitive response of LSPR with the change of surrounding media refractive indices, this technique can convert the refractive index variation to the scattering intensity difference and form a high contrast, diffraction limited image of a thin unstained transparent specimen with small refractive index variation

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