Nomarski's Differential Interference Contrast Microscope
The Nomarski microscope uses a Wollaston prism in the illumination path to produce two orthogonally polarized, slightly shifted bright spots at the sample's surface. Upon reflection from (or transmission through) the sample, the two beams are collected by the objective lens, then sent through the same (or, in the case of a transmission microscope, a similar) Wollaston prism, which recombines the two beams by sliding them back over each other. The two beams subsequently arrive coincidentally in the image plane of the microscope, but the two images of the sample, which they carry, will be relatively displaced. A linear analyzer, placed after the Wollaston prism in the reflected (transmitted) path, brings the polarization vectors of the two images into alignment, enabling the two to interfere with each other. A sheared interferogram of the sample's surface is thus formed at the image plane of the microscope.
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