interference microscope

(optics) A microscope used for visualizing and measuring differences in phase or optical paths in transparent or reflecting specimens; it differs from the phase contrast microscope in that the incident and diffracted waves are not separated, but interference is produced between the transmitted wave and another wave which originates from the same source.

An instrument for visualizing and measuring differences in the phase of light transmitted through or reflected from microscopic specimens. It is closely allied to the phase-contrast microscope. See also Phase-contrast microscope.

A microscopic image is formed by the interaction of all light waves passing through the optical system. In a phase-contrast microscope, light diffracted by a transparent object is spatially separated from nondiffracted light in the back focal plane of the objective, where a phase plate alters the relative phases of the diffracted and nondiffracted beams so that they interfere in the image plane to produce a visible, intensity-modulated image. In an interference microscope, the diffracted and nondiffracted waves are not spatially separated, but light (the object beam) that passes through or is reflected from the object interferes with light (the reference beam) that passes through or is reflected from a different region of the specimen plane or is reflected from a comparison (reference) surface. For interference to be visible, the light beams must be coherent; in other words, the beams must maintain a constant relationship of wavelength, phase, and polarization over a relatively long period. The easiest way to achieve coherence is by using a device such as a semireflecting mirror, which splits a light beam into two beams. Random changes in the properties of successive photons from a given point in the source then affect both beams simultaneously. Differences in optical path introduced by various parts of the object can be seen as variations in intensity or color. See also Interference of waves.

A microscope designed to split entering light into two beams that pass through the specimen and are recombined in the image plane, allowing visualization of refractile object details that are not possible with a single beam.