Improved averaging for non-null interferometry

Jon F. Fleig; Paul E. Murphy

doi:10.1117/12.2028780

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15 October 2013 Improved averaging for non-null interferometry

Jon F. Fleig, Paul E. Murphy

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Proceedings Volume 8884, Optifab 2013; 88840Z (2013) https://doi.org/10.1117/12.2028780
Event: SPIE Optifab, 2013, Rochester, New York, United States

Abstract

Arithmetic averaging of interferometric phase measurements is a well-established method for reducing the effects of time varying disturbances, such as air turbulence and vibration. Calculating a map of the standard deviation for each pixel in the average map can provide a useful estimate of its variability. However, phase maps of complex and/or high density fringe fields frequently contain defects that severely impair the effectiveness of simple phase averaging and bias the variability estimate. These defects include large or small-area phase unwrapping artifacts, large alignment components, and voids that change in number, location, or size. Inclusion of a single phase map with a large area defect into the average is usually sufficient to spoil the entire result. Small-area phase unwrapping and void defects may not render the average map metrologically useless, but they pessimistically bias the variance estimate for the overwhelming majority of the data. We present an algorithm that obtains phase average and variance estimates that are robust against both large and small-area phase defects. It identifies and rejects phase maps containing large area voids or unwrapping artifacts. It also identifies and prunes the unreliable areas of otherwise useful phase maps, and removes the effect of alignment drift from the variance estimate. The algorithm has several run-time adjustable parameters to adjust the rejection criteria for bad data. However, a single nominal setting has been effective over a wide range of conditions. This enhanced averaging algorithm can be efficiently integrated with the phase map acquisition process to minimize the number of phase samples required to approach the practical noise floor of the metrology environment.

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Jon F. Fleig and Paul E. Murphy "Improved averaging for non-null interferometry", Proc. SPIE 8884, Optifab 2013, 88840Z (15 October 2013); https://doi.org/10.1117/12.2028780

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