Active optics module for SPHERE

The  VLT-SPHERE instrument, dedicated to exoplanets direct imaging, benefits of one of the developments made in the team, regarding the stress polishing of super-smooth off axis mirrors.

Three off axis toric mirrors are  placed at the core of the instrument, in the adaptive optics module, to relay the beam  without introducing high spatial frequency errors that could degrade the final contrast in the instrument.

Fruit of the R&D activities undertaken during the last ten years (Hugot+2009, Hugot+2012), we delivered these mirrors with an extreme smoothness (less than 2nm RMS of local errors, less than 0.5nm roughness). Please follow this link for the ESO press release.

One of these mirrors (the biggest) is now equipped with a warping harness, for the real time bending of the surface in order to compensate  for the undesired shape at rest of the deformable mirror.  (See this post)

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The three off axis toric mirrors, super-polished under stress, at the core of the SPHERE extreme adaptive optics module

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Interferograms of the three mirrors, showing the extreme smoothness obtained with the stress polishing with full sized laps.