Interferometric measurement of local radii of curvature for aspheric surface using a PDI

One of the problems that have manufacturers of aspheric and freeform surfaces is the local measurement of the shape, in order to ensure the performance of the surface. In this paper we present an alternative method to measure local radii of curvature of systems with symmetry revolution, using the Point Diffraction Interferometer technique (PDI). To implement this proposal a certified plane wavefront is used as reference light source, and the PDI as sensor element for measuring the local radii of curvature. We proposed to use a PDI due to its high sensitivity because is a common path interferometer and generate interference only when there is an only point a single convergence which is produced from an annular region of the surface, and the annular region is associated to each local curvature center. Experimental results are shown for one aspherical surface with different rates of change in their slopes for each region of the surface, showing the versatility of the proposal and its possible use, including free-form surfaces without symmetry of revolution.