Interferometry is based on the wave properties of the light. A light beam is divided into a reference and an object beam. The beams are reflected back and combined in a beam combiner. The two waves interfere and form a fringe pattern. The pattern shows the difference in the optical path length between the reference and the object arm and is coded by the wavelength of the light. Parameters as shape and deformation of the object can be measured. Also periodic movements of the surface can thus be detected and quantified.