Browsing by Author "Fouche, Eugene Egbert"

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    Fourier ptychographic microscopy for high-resolution, large field of view imaging
    (Stellenbosch : Stellenbosch University, 2023-12) Fouche, Eugene Egbert; Neethling, Pieter H. ; Bosman, Gurthwin W. ; Stellenbosch University. Faculty of Science. Dept. of Physics.
    ENGLISH ABSTRACT: Fourier ptychographic microscopy (FPM) is an imaging technique which overcomes the limitations of conventional microscopy to construct high-resolution, large field of view (FOV) images of a sample. Usually, there is a trade-off between resolution and field of view, but FPM allows samples to be viewed at a high resolution, while maintaining a large FOV. FPM is a computational imaging technique, where multiple low-resolution images of a sample are used to reconstruct the sample at a much higher resolution. The sample is illuminated from various angles, and a low-resolution image is captured for each illumination angle using a lens with a low numerical aperture (NA). The low NA lens has a large FOV, and the various illumination angles allows one to obtain information about the smaller sample features. This allows one to reconstruct a high-resolution, large FOV image of the sample using an iterative reconstruction algorithm. An LED array is typically used to provide the angularly varying illumination. Many real-world samples alter both the amplitude and the phase of the light that is transmitted through them. However, only the intensity can be measured on a camera, and the phase information is lost. In FPM, the various sample images allows one to recover the phase of the sample, as well as the amplitude. This can be used to correct for errors in the imaging setup, and also enhances the contrast when viewing biological samples. In this thesis, the theoretical framework behind FPM is explained, and simulations are performed to investigate the effect of the LED array size and the number of iterations of the reconstruction algorithm on the quality of the reconstructed sample. The error correction (defocus aberration) is also investigated. Two setups are constructed to investigate FPM experimentally. The first setup uses an LED array, and is used to image known calibration targets and real-world biological samples. This setup is also adapted to perform polarization-sensitive FPM (pFPM) on birefringent mineral samples to image the different crystal domains in the samples. The second setup uses a continuous wave laser as the light source and a 2-dimensional spatial light modulator (2D-SLM) to provide the angularly varying illumination. This setup is used to image a known calibration target. Both setups are characterised, and their performance is compared to illustrate their suitability for different imaging scenarios.