ABSTRACT
Early phase-shifting interferometric techniques can be traced back to Carré, but their further development and application were later reported by Crane, Moore, and Bruning among others. In phase-shifting interferometers, the reference wavefront is moved along the direction of propagation with respect to the wavefront being analyzed, thus changing the phase differences. The transducer moves the mirror so the phase is changed to a new value. The best focus is defined as the focus setting that minimizes the absolute value of the maximum radial slope over the pupil. Another method for shifting the phase is to insert a planeparallel glass plate in the light beam. A Ronchi ruling moving perpendicularly to its lines in the Ronchi test is a particular case of a moving diffraction grating. The first quarter-wave retarding plate is stationary, with its slow axis located at 45° with respect to the plane of polarization of the incident linearly polarized light.
