Arun Anand
(University of Baroda)
 

Brightfield microscopy is an ideal tool for observing micro-objects, including living cells, under various conditions. Information obtained from the microscope can be used to characterize, identify, and compare cells. It is still a gold standard in identification of many diseses and health conditions including malaria, sickle cell disease, thalassemia etc. However, since many living cells have low absorption cross-section for visible light bright field microscopes provide only low contrast 2D images. Also, no information about cell morphology is accessible. Phase contrast microscopy techniques provide a way to overcome the problem of low contrast. Also, if direct access to the phase of the object wavefront is available, cell thickness distribution (cell morphology) can be reconstructed. This leads to quantitative phase microscopy (QPM). The phase of the object wavefront (wavefront interacting with the object or sample under test) can be retrieved by superposing it with a reference wavefront (wavefront unmodulated by object information). Object phase information is encoded in the interference fringes resulting from the superposition of the two wavefronts (object and reference). Digital holography is one of the techniques for quantitative phase imaging, where holograms (interference patterns) are recorded on semiconductor arrays and reconstructed by the numerical implementation of scalar diffraction integrals. This yields the complex amplitude distribution of the object wavefront. The phase of the object wavefront is extracted from the complex amplitude and then converted into thickness distribution. QPM using digital holography is a single-shot technique that provides cell thickness information of the entire cell from a single hologram, yielding many sample features based on sample thickness and its time variation. The presentation will provide an overview of our work on designing and developing compact, portable, low-cost digital holographic microscopes for label-free quantitative phase imaging of technical and biological samples.

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