Abstract

The automatic reduction of single test interferograms is typically done by ridge following algorithms. The effect of this approach is to smooth high frequency structure in the surface, on a scale less than the fringe separation. We have developed a new algorithm that involves no smoothing and is very fast. The result for any individual interferogram contains errors of ± λ/20 in the wavefront, but when reductions of many interferograms with random piston errors in phase are combined, these errors average out. This method will be especially valuable for the metrology of very large telescope mirrors, when seeing in a large test tower is likely to give as large errors as the algorithm error, and vibration is likely to compromise phase shifting analysis methods. Preservation of high spatial frequency information is especially valuable for telescope mirrors, whose tolerance is of order 0.02 waves rms surface error on a scale of 5 cm.

© 1986 Optical Society of America