Fourier holography for wide-field characterisation of microstructures

[Truncated abstract] Biomedical imaging with light can provide very high-resolution images, however, the field of view and working distance are generally limited and decrease with increasing resolution. In many cases additional staining or labelling of specific sample features is required to enhance the visibility of certain features. This thesis presents two wide-field, high-resolution optical imaging approaches developed to overcome such previously mentioned limitations by combining innovative optical system design with digital holographic recording and intelligent processing algorithms. The first technique we have called "Spatially resolved Fourier holographic angular scattering spectroscopy". A single hologram permits the characterisation of particle sizes in a known medium by examining their elastic light scattering spectra as a function of scattering angle. The directly reconstructed, low-resolution sample image is used to create a map of size distributions. Localised size information is extracted from the angular spectroscopic data, which is more sensitive to changes in particle size than the image reconstructions. We have demonstrated the two-dimensional characterisation of thin samples, containing microspheres with diameters between 5 μm and 12 μm or red blood cells, over an area of 3 x 3 mm. We have extended the technique to three-dimensional particle sizing, which has been shown for a volume of 3 x 3 x 2 mm. A multiple-exposure extension of this technique has been developed to extend the range of detectable particle sizes to 2 μm and, at the same time, improve sizing sensitivity. Biomedical applications could include the investigation of cancerous tissues or the dynamic study of micrometre-scale changes in large volumes.