Sub-Nyquist Interferometry: Results and Implementation Issues

Phase-shifting interferometry (PSI) is the generally accepted technique for data acquisition and computer analysis of interferometric patterns. General purpose instruments that use this technique for the measurement of spheres and flats are available from a number of vendors. Recent improvements in the fabrication of aspheric surfaces have led to interest in a similar instrument for the measurement of aspheric surfaces. This instrument must be able to measure large departures from a reference surface, which is a limitation of PSI. Sub-Nyquist interferometry (SNI) extends the range of PSI by using a priori knowledge of the test surface. This paper will review SNI, discuss its hardware implementation, and give the results of preliminary wavefront analysis.