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Quantitative phase microscopy (QPM) is a label-free imaging technique to quantify various biophysical parameters, such as refractive index, optical thickness, cell dry mass, and dynamic membrane fluctuations. Accurate determination of these parameters requires the use of a QPM system with high temporal phase stability and high spatial phase sensitivity. We report a QPM system based on a common-path interferometer with high temporal phase stability and high spatial phase sensitivity. The proposed QPM system is highly temporally stable, compact and easy to align and implement. The interference pattern can be obtained quickly even with a low coherent light source. In order to realize high spatial phase sensitivity, we used partially spatially coherent (pseudo-thermal) light source for illumination. Due to the partial spatial coherent nature of the light source, a speckle-free interferogram/hologram is recorded over the entire field-of-view. Two types of speckle free QPM systems are implemented using common path Fresnel biprism as well as lateral shearing interferometers. A Fresnel biprism is used in the self-referencing mode, thus offering the advantage of no optical power loss in addition to high temporal stability and the least speckle artifacts. Furthermore, it is very easy to implement, as the system completely replaces the need for spatial filtering at the source end as well as for the reference beam generation. In another configuration, we used a lateral shearing interferometer. The scattered light from the object is collected by the microscope objective lens and passes through a 4mm thick optically flat parallel plate to generate the interference pattern. Phase maps of human RBCs are reconstructed and the results are compared for fully and partially coherent light illumination.
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