In general, an interferometer may consist of coherent source split into a’ signal’ beam and a ‘reference’ beam, with irradiances I1 and I2, respectively. The signal beam carries information about surface/thickness of the test object. By bouncing the signal beam off of the test object (highly reflective objects) or passing it through (transparent objects) the object, the phase of the signal beam is altered according to the surface (or thickness) variations of the object.