Micrometric noncontact profiler for optical quality surfaces

A non-contact technique for obtaining accurate profiles of optical qualitysurfaces with micrometric accuracy has been developed. The technique isbased on the Ronchi test principle, that is, on the study of the interaction of awavefront reflected on the surface to be profiled with a square-wavetransmittance ruling. From the resultant fringe pattern and some basicgeometrical optics principles it is possible to measure the local normal to thesurface being tested at a set of given points. This local normal map may thenbe integrated, yielding the surface profile. By use of a theoretically expectedsurface shape, the main parameters of the surface may then be determined bysurface fitting of the measured data to that expected surface shape. Resultsof the profilometric measurements both of a spherical and of a toroidalsurface are presented. The measured profiles are validated by comparison ofthe radii of curvature obtained using a high precision radioscope with theones obtained by surface fitting of the measured profiles to their expectedsurface shapes. Additionally, subtracting the best-fit theoretical surface fromthe measured profile allows the observation of surface deviations from thetheoretical shape to within some tenths of a nanometres.Peer ReviewedPostprint (published version