Michelson interferometer
The fixed mirror in the Michelson interferometer is rotatable in the Twyman–Green interferometer, and while the light source is usually an extended source (although it can also be a laser) in a Michelson interferometer, the light source is always a point-like source in the Twyman–Green interferometer. The rotation of one mirror results in straight fringes appearing in the interference pattern, a fringing which is used to test the quality of optical components by observing changes in the fringe pattern when the component is placed in one arm of the interferometer.