Quantitative Phase Signal (QPS) stems from the difference between the refractive indices of the observed specimen and that of its surrounding environment (ne). Therefore, any change in ne will drastically affect the QPS. We have developed an original approach, based on both the manipulation and the measurement of ne that allows from the QPS the visualization of various structures inside the observed specimen as well as accurate measurements of their respective refractive indices. Such an approach performed with digital holographic microscopy on living cells reveals internal cell structures including organelles (nucleus, nucleolus, vesicles, etc.) and some components of the cytoskeleton.
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