Classical interference microscopy

Classical interference microscopy, also called quantitative interference microscopy, uses two separate light beams with much greater lateral separation than that used in phase contrast microscopy or in differential interference microscopy (DIC). In variants of the interference microscope where object and reference beam pass through the same objective, two images are produced of every object (one being the "ghost image").

Source: Wikipedia — Classical interference microscopy (CC BY-SA 4.0)