Testing aspherics using two-wavelength holography: use of digital electronic techniques

Two-wavelength holography has been shown to be quite useful for testing aspheric surfaces since it can produce interferograms with a wide range of sensitivities. However, TWH has the drawback that the accuracy attainable from measurements on photographs of the fringes is limited. It is shown how this limitation can be overcome by using digital electronic techniques to evaluate the phase distribution in the interference pattern.