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6. Conclusion

This is the first time that a variable curvature mirror is achieved with such a large range. Using large deformations theory, the maximal flexion achieved from the initial plane figure, is close to 1200 He-Ne fringes.

The achieved optical quality is in accordance with the ESO requirements for a 3.5 arcsec FOV (WFE tex2html_wrap_inline1187 on a 6 mm diam.) and leads to the realization of a VCM system fulfilling its goals in the forthcoming optical interferometric array of the VLT. The manufacturing process now represents the limit of the technology. If a wider FOV of 8'' is planned, we will have to consider a larger active mirror in order to achieve the required optical quality on a 14 mm diameter, this can be obtained by using a 28 or 30 mm mirror. Today this VCM system is being included in the delay-line system in order to setup and calibrate the interfaces with the other devices of the interferometric mode. A gold coating, easy to apply on a stainless steel substrate, has been done on the first sample delivered to ESO in order to increase the reflectivity of the mirror. The integration will be done during this year, and the installation on the Paranal observatory of the first complete system (delay-line with VCM) will occur around year 2000. The VLTI will not be the only interferometer to benefit of this type of device, as recently such a VCM system has been choosen to be used in another optical interferometric array. Variable curvature mirrors will be part of the upgraded Grand Interferometer à 2 Telescopes (GI2T) of the Observatoire de la Côte d'Azur, located in Plateau de Calern.



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