Calibration concepts for the MUSE integral field

The phase-A design study of the Calibration Unit (CU) for the Multi-Unit Spectroscopic Explorer (MUSE) is presented. MUSE is an integral-field spectrograph for the 2nd generation of VLT instruments and offers a relative wide integral-field, adaptive-optics assisted spatial resolution, and a wavelength coverage between 465 and 930 nm. MUSE is a project of seven European institutes and is led by the Centre de Recherche Atronomique de Lyon (CRAL). Amongst other work-packages, the Astrophysical Institute Potsdam (AIP) is responsible for the Calibration Unit. The paper describes the calibration requirements, including issues related to spectral, image quality, and geometrical calibration. The opto-mechanical layout of the calibration unit is presented and the use of focal plane masks to evaluate image distortions and PSF degradations is explained.