An apparatus that reunites two or more electromagnetic or sonic wave
coming from the same source via different paths, to produce interference between them.
Adding to the optical interferometer, X-rays, electron beam, and
ultrasonic interferometer are also used. Interferometers are effective to measure small
displacements or subtle differences in reflective index, and are used to measure surface geometry,
deformation, displacement, vibration, changes in density. Typical optical interferometers are
Michelson interferometer, Twyman-Green interferometer, Fizeau interferometer, Mach-Zehnder
interferometer, shearing interferometer, and Fabry-Perot interferometer.