Design of an integral field unit for MUSE, and results from prototyping

摘要

The research and development activity on image slicer systems for integral field spectroscopy has increased in recent years, allowing the simultaneous observation on the same detector matrix of two-dimensional sky maps and the spectral decomposition of light. Nowadays, image slicers lead to possible applications on future instrumentation for ground- and space-based telescopes, covering a spectral domain ranging from UV to mid-IR wavelengths. Among such projects, MUSE ( Multi Unit Spectroscopic Explorer) is an integral field spectrograph proposed by the European Southern Observatory for its second-generation Very Large Telescope instrumentation. MUSE combines a 1' x 1' field of view, with a spectral resolution reaching 3000 and a spatial sampling of 0."2 provided by an adaptive optics system. MUSE operates in the visible and near-IR wavelength range (0.465 - 0.93 mu m) and is composed of 24 identical integral field units; each one incorporates an advanced image slicer made up of a combination of mirrors and "minilens" arrays, a spectrograph, and a detector. This paper describes the optical design of the MUSE image slicer, which complies with top-level requirements at a reasonable cost. The optical manufacturing technique, based on an original method of assembly using molecular adhesion, is presented. Finally, we focus on the optical tests of the prototype both at a system level and at the level of individual optical elements.