Most interferometers are optical interferometers, which means that it is light waves that are used and analysed. Examples of other types of interferometers that use other waves forms are the atom interferometer, which uses atoms, and the Interferometric synthetic aperture radar (InSAR), which uses radiation.
Optical interferometers work splitting a beam of light into two using mirrors/lenses. The resulting waves are then combined again to create interference and then the result observed and measured. During the early days of interferometry scientists only used white light sources but now there are interferometers that use even monochromatic light sources like laser. Some of the common kinds of optical interferometers include the Michelson interferometer, Mach-Zehnder interferometer, Sagnac interferometer, and Fabry-Perot interferometer. The Michelson interferometer, which is one of the most basic interferometers, is probably the most popular interferometer having been used to prove Einstein’s Theory of Relativity.