Cold optics of MIDi: the mid-infrared interferometric instrument for the VLTI

摘要

ESO's new Very Large Telescope will consist of four 8.2m telescopes and three moveable 1.8m telescopes. Light from these can be combined in the Very Large Telescope Interferometer (VLTI) providing milli-arcsecond resolution with high sensitivity. The VLTI will first operate in the infrared and will produce first fringes in 2001. MIDI is the VLTI instrument for interferometry int eh mid-infrared (10-20 microns) and is under development by a German-Dutch-French consortium (MPIA Heidelberg, NOVA/NFRA Netherlands, Observatoire Meudon France). The initial aim of MIDI is to combine the beams of two telescopes in the 10 micron `N-band' and to achieve spatial resolutions of 20 milli-arcseconds at a spectral resolution of 200-300. Modulation of the optical path difference can be done using piezo-driven mirrors at room temperature, but beam combination and detection of the interferometric signal has to be done at cryogenic temperatures due to the `thermal' wavelength domain. The MIDI cold bench is therefore mounted inside a cryostat, cooled by means of a closed cycle cooler to about 40K for the cold optics and 8 K for the detector. This poster describes the design and implementation of the MIDI cold bench.