Abstract
A non-contact technique for obtaining accurate profiles of optical quality surfaces with micrometric accuracy has been developed. The technique is based on the Ronchi test principle, that is, on the study of the interaction of a wavefront reflected on the surface to be profiled with a square-wave transmittance ruling. From the resultant fringe pattern and some basic geometrical optics principles it is possible to measure the local normal to the surface being tested at a set of given points. This local normal map may then be integrated, yielding the surface profile. By use of a theoretically expected surface shape, the main parameters of the surface may then be determined by surface fitting of the measured data to that expected surface shape. Results of the profilometric measurements both of a spherical and of a toroidal surface are presented. The measured profiles are validated by comparison of the radii of curvature obtained using a high precision radioscope with the ones obtained by surface fitting of the measured profiles to their expected surface shapes. Additionally, subtracting the best-fit theoretical surface from the measured profile allows the observation of surface deviations from the theoretical shape to within some tenths of a nanometres.
Export citation and abstract BibTeX RIS