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27 July 2010 Development and performance of the EAGLE active optics LGS WFS refocusing system
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We designed, developed, and tested a Variable Curvature Mirror (VCM) as an active refocusing system for the Laser Guide Star (LGS) Wave Front Sensor (WFS) of the E-ELT EAGLE instrument [1]. This paper is the second of two from our team on this R&D activity: Hugot et al. this conf. [2] presented the mirror design and performance simulations. Here, we report on the fabrication integration, testing and performance of the VCM system. During this activity, we developed all necessary parts for the VCM system: a metallic mirror, its housing and mounts, a computer-controlled pressure system, an internal metrology, a testbench etc. The functional testing of the VCM system is successful: we can control the internal pressure to less than 1 mBar, and measure the mirror displacement with a 100 nm accuracy. The mirror displacement is a near-linear and well-simulated function of internal pressure for the desired range of focus. The intrinsic optical quality of the mirror meniscus is well within the specifications. Once mounted in its housing, we observe additional mechanical constraints for the current design that generate optical aberrations. We measured the amplitude of the Zernike modes, and we showed that the axisymetric terms display a variation trend very similar to simulations, with amplitude close to simulations. All these results are very promising for a design of focus compensation without any moving part.
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Fabrice Madec, David Le Mignant, Elodie Chardin, Emmanuel Hugot, Silvio Mazzanti, Jean-Luc Gimenez, Marc Ferrari, Gabriel Moreaux, Sébastien Vives, and Jean-Gabriel Cuby "Development and performance of the EAGLE active optics LGS WFS refocusing system", Proc. SPIE 7736, Adaptive Optics Systems II, 773638 (27 July 2010); doi: 10.1117/12.857008;


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