Differential Interference Contrast, an optical microscopy technique in which light transmitted through a sample is first polarized, then split into two polarizations slightly displaced from one another, sent through the sample, and subsequently recombined to form an image. One of the beams is typically retarded relative to the other by some fraction of a wavelength; if there is further relative retardation between the two beams, for example when beam 1 hits a feature with a higher index of refraction than beam 2, then the two beams will interfere more or less constructively, resulting in a change in intensity at that point in the image. The resulting image reflects changes in the index of refraction of the sample along the beam split axis, at the focal plane. It results in a much higher contrast image which can resolve much finer details, and is very popular with biologists, among others.