Interferometry

Interferometers such as Michelson's can be used for many types of measurements. As a spectrometer, they can be used to accurately measure the mirror #1 mounted on a motor, so it can be moved along the direction of the beam at a constant speed. As the mirror moves, a fringe at a point in the interference plane will appear as an alternating Figure 3. Top view of the Sagnac cyclic interferometer. Illustration by Hans & Cassidy. Courtesy of Gale Group. bright and dark band. The frequency of the changing fringes is related to the wavelength, and can be calculated to better than several parts in 100 billion.