The Michelson interferometer is a common configuration for optical interferometry and was invented by Albert Abraham Michelson. Using a beamsplitter, a light source is split into two arms. Each of those is reflected back toward the beamsplitter which then combines their amplitudes interferometrically

A laser falls on a beam splitter, which allows half of the light to pass straight through, and reflects the other half downward. Each of those beams then hits a mirror that reflects it directly back where it come from. The beams are recombined at the beam splitter, and then fall on the viewing screen at the top of the figure.
When we add together the light from the two paths, we find that if the lengths of the two arms (that is, the distance from beam splitter to mirror) are exactly the same, then we see a bright spot on the viewing screen that is as bright as the original laser (this is called “constructive interference”). If we move the right-hand mirror back by one half of the wavelength of the laser, we see no light at all on the viewing screen (“destructive interference”).

Application of Michelson Interferometer -:Gravitational wave detection
Michelson interferometry is one leading method for the direct detection of gravitational waves. This involves detecting tiny strains in space itself, affecting two long arms of the interferometer unequally, due to a strong passing gravitational wave. In 2015 the first detection of gravitational waves was accomplished using the LIGO instrument, a Michelson interferometer with 4 km arms. This was the first experimental validation of gravitational waves, predicted by Albert Einstein’s General Theory of Relativity.