Slicing the universe at affordable cost:: The quest for the MUSE image slicer

The introduction of Image Slicers in Astronomy has been growing rapidly in the recent years. These optical devices allow the simultaneous observation on the same detector matrix of two-dimensional sky maps and the spectral decomposition of light on all of their angular samples, therefore dramatically reducing the observation times and getting rid of the spectrophotometric variations of the atmosphere. Today the implementation of Image Slicers is planned on various ground and space telescopes, covering a spectral domain ranging from blue to mid-IR wavelengths. Among such different projects, we describe the Image Slicer of MUSE (Multi Unit Spectroscopic Explorer), a second-generation Integral-Field Spectrograph for the VLT combining a 1' x 1' Field of View with a spatial resolution of 0.2" and a spectral resolution of 3000. The most efficient principle of an Image Slicer consists in a combination of several different optical channels, each made of three mini-mirrors having different tilts and curvatures. After a brief presentation of the MUSE Image Slicer requirements, we will explain the followed logic in order to optimise the opto-mechanical design and cost of the Slicer : indeed one of MUSE peculiarity is the total number of its individual modules, that is 24. The realization of such series at an affordable cost actually is a design driver of the study. The communication also deals with the used optical design models, the expected performance, the candidate technologies for the manufacturing of all the components, and the future development of a prototype of this critical optical subsystem.