15 October 2013 Wavefront measurements through optical diffraction interpretation
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Proceedings Volume 8884, Optifab 2013; 888428 (2013) https://doi.org/10.1117/12.2028876
Event: SPIE Optifab, 2013, Rochester, New York, United States
Abstract
The French Laser MégaJoule (LMJ) will include 176 square beams involving hundreds of large optical components. Wavefront performances of all these components are critical to achieve the desired focal spot shape and to limit hot spots that could damage the components. These specifications are usually checked with interferometric setups. This can be uneasy to achieve for specific components such as multi-dielectric mirrors or gratings because one has to use the exact nominal configuration (wavelength, incidence, geometry of the incident beam) to perform the measurement. For the smallest spatial periods, classical techniques like interferometric microscopes fail to measure the wavefront and propose a "surface" measurement that can lead to misinterpretations. We present in this paper measurement methods based on a laser beam diffraction interpretation that can efficiently replace the usual techniques. The first technique consists in measuring intensity level of the dim scattered "corona" around the focal spot. The second one is based upon image processing of near-field acquisitions by the means of Fourier analysis and the Talbot effect theory. Those techniques do not lead to a phase map as classical techniques do but they give access to the Power Spectral Density of wavefront defects over a large spatial frequency bandwidth. For many applications, this is enough information to estimate the component performance. We present results obtained by this way on LMJ components and a comparison with Fizeau interferometer measurement.
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Stéphane Bouillet, Stéphane Bouillet, Sandrine Chico, Sandrine Chico, Laure Eupherte, Laure Eupherte, Claude Rouyer, Claude Rouyer, Jérôme Daurios, Jérôme Daurios, } "Wavefront measurements through optical diffraction interpretation", Proc. SPIE 8884, Optifab 2013, 888428 (15 October 2013); doi: 10.1117/12.2028876; https://doi.org/10.1117/12.2028876
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