Mastering the effects of air turbulence in optical components interferometric metrology

Manuel Mestre; Frank A. DeWitt IV

doi:10.1117/12.2603288

28 October 2021 Mastering the effects of air turbulence in optical components interferometric metrology

Manuel Mestre, Frank A. DeWitt IV

Proceedings Volume 11889, Optifab 2021; 118890E (2021) https://doi.org/10.1117/12.2603288
Event: SPIE Optifab, 2021, Rochester, New York, United States

Abstract

Air turbulence is a major environmental factor that degrades the precision of optical part interferometric metrology. For large optics with a long cavity, turbulence effects become critical. Reducing those effects by protecting the cavity with mechanical means is necessary, though not sufficient. Averaging wavefronts is a simple, classic, and efficient remedy. However averaging leaves unanswered the following issues: How many wavefronts should be averaged? What is the resulting uncertainty on the parameters of interest (RMS, PTV...)? What is the risk for a parameter to be over tolerance? For addressing those issues, the Xonox X-fringe® interferometry software is fitted with an advanced "Average Statistics" function. Reading a given number of phase data maps, the function computes the average phase map and estimates the significant statistical characteristics of the turbulence, namely its space and time auto-correlation function (ACF), as well as the ACF of the sample average. The latter provides a covariance matrix, applied to Monte-Carlo random trial simulations. On each of those random trials, a parameter of interest is computed. For a high number of trials, the frequency histogram of this parameter tends towards its probability density. Finally, this density yields confidence intervals of the parameter (i.e., uncertainty with a confidence level), and above all, the risk that the parameter could be over tolerance. The user can create templates defining, for a given set of Zernike, the parameter of interest (PTV, RMS, Strehl), or that of the residual wavefront. The software evaluates the signal-to-noise ratio and the measurement reliability.

Conference Presentation

Citation Download Citation

Manuel Mestre and Frank A. DeWitt IV "Mastering the effects of air turbulence in optical components interferometric metrology", Proc. SPIE 11889, Optifab 2021, 118890E (28 October 2021); https://doi.org/10.1117/12.2603288

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