Optical Design of Volume Holographic Imaging Systems for Microscopy

Abstract

Confocal microscopy rejects out of focus light from the object by scanning a pinhole through the object and constructing the image point by point. Volume holographic imaging (VHI) systems with bright-field illumination have been proposed as an alternative to conventional confocal type microscopes. VHI systems are an imaging modality that does not require scanning of a pinhole or a slit and thus provides video rate imaging of 3-dimensional objects. However, due to the wavelength-position degeneracy of the hologram, these systems produce less than optimal optical sectioning because the high selectivity of the volume hologram is not utilized. In this dissertation a generalized method for the design of VHI systems applied to microscopy is developed. Discussion includes the inter-relationships between the dispersive, degenerate, and depth axes of the system. Novel designs to remove the wavelength-position degeneracy and improve optical sectioning in these systems are also considered. Optimization of a fluorescence imaging system and of dual-grating confocal-rainbow designs are investigated. A ray-trace simulation that integrates the hologram diffraction efficiency and imaging results is constructed and an experimental system evaluated to demonstrate the optimization method. This results in an empirical relation between depth resolution and design tolerances. The dispersion and construction tolerances of a confocal-rainbow volume holographic imaging system are defined by the Bragg selectivity of the holograms. It is found that a broad diffraction efficiency profile of the illumination hologram with a narrow imaging hologram profile is an optimal balance between field of view, construction alignment, and depth resolution. The approach in this research is directly applicable towards imaging ovarian cells for the detection of cancer. Modeling methods, illumination design, eliminating the wavelength degeneracy of the hologram, and incorporating florescence imaging capability are emphasized in this dissertation. Results from this research may be used not only for biomedical imaging, but also for the design of volume holographic systems for both imaging and sensor applications in other fields including manufacturing (e.g. pharmaceutical), aerospace (e.g. LIDAR), and the physical sciences (e.g. climate change).