Stitching interferometry for the measurement of aspheric surfaces

In this paper, we describe the progress being made in the development of stitching interferometry for measuring curved surfaces with large aspheric departures. Stitching interferometry is an extension of conventional interferometry by making a series of submeasurements and then stitching the surface segments together to obtain an entire reconstructed surface. We have implemented it by modifying a phase shifting interferometer with a mechanical manipulator for shifting and/or rotating the workpieces under test precisely. An outline summarising the principles and the algorithms developed, to correct the aberrations introduced by the misalignment of the submeasurements and the misregistration of the individual data sets, is presented. The technique offers considerable potential applications for testing precision surfaces with large aspheric departures