MAVIS adaptive optics module optical design

The MCAO Assisted Visible Imager and Spectrograph (MAVIS), is a new instrument for ESO’s Very Large Telescope. The instrument will be installed at the Nasmyth focus of the UT4 telescope and is comprised of an imager and a spectrograph which will take advantage of the unprecedented angular resolution and sky coverage provided by LGS assisted MCAO correction at visible wavelengths. The Adaptive Optics Module (AOM) is the core engine of MAVIS, devoted to multi-conjugate wavefront sensing and correction, and designed to deliver a 30×30 arcsec2 corrected field of view to the scientific instruments. In this paper we focus on the optical design of the AOM, which has been optimized to perform several tasks including field de-rotation, atmospheric dispersion correction, and adaptive optics closed-loop operations. To maximize sky coverage, the system is designed to deliver a 2 arcmin field of view for the selection of up to 3 NGS for measurement of tip-tilt. The AOM module also includes a multiple LGS WFS for high-order wavefront measurements and two post-focal DMs for wide field turbulence compensation. The proposed design is the result of a trade-off study in which particular care has been devoted to satisfy performance and operational requirements, as well as modularity. We present here a complete description of the selected optical configuration with a summary of the performance analyses.