Oblique incidence interferometry applied to non-optical surfaces

This paper demonstrates the use of transmitting diffraction gratings as beamsplitters in an oblique incidence interferometer and the application of that interferometer to measuring the flatness of non-optical surfaces. Many different surfaces have been examined, ranging from lapped granite and steel to unworked metal and processed photographic emulsions. The fringe interval in the interferograms is independent of the illuminating wavelength, being one half of the diffraction grating periodicity, which in the interferometer described is 5 mu m. It is also demonstrated that the topography of large surface areas may be evaluated by the combinations of interferograms.