A type of light microscope that is useful for viewing live transparent unstained specimens, such as cells or microscopic organisms. The shadow-cast images give the illusion of depth to the outlines and surface features of organelles or other structures. An incident beam of plane-polarized light is split into parallel beams by a prism (Nomarski prism; a development of the Wollaston prism) so that different parts of the beam pass through closely adjacent areas of the specimen. Slight differences in thickness and refractive index within the specimen cause interference between the beams as they exit the specimen and are recombined by a second prism: parts of the beam that are in phase will reinforce each other and produce a bright image, whereas parts that are out of phase will cancel each other out and produce a dark image. It is named after the Polish-born physicist Georges Nomarski (1919–97), who devised it in the mid-1950s.

https://www.olympus-lifescience.com/en/microscope-resource/primer/techniques/dic/dicoverview/ An overview of Nomarski microscopy with an interactive tutorial, from the Olympus Microscopy Resource Center