ESO VISIR Astronomical Filter Consortium

2000 - 2004

Astronomical Filter ConsortiumProject overview

The VISIR instrument for the European Southern Observatory (ESO) Very Large Telescope (VLT) is a thermal-infrared imager and spectrometer currently being developed by the French Service d'Astrophysique of CEA Saclay, and Dutch NFRA ASTRON Dwingeloo consortium. This cryogenic instrument will employ precision infrared bandpass filters in the N-(λ=7.5-14µm) and Q-(λ=16-28µm) band mid-IR atmospheric windows to study interstellar and circumstellar environments crucial for star and planetary formation theories.

The infrared filters and coatings developed for the VISIR spectrometer and imager have attracted interest from other ground-based observational telescopes requiring filters in the N- and Q-band wavelength regions, namely;

  • W.M. Keck-LWS
  • AURA-Gemini
  • GTC-CanariCam

All these institutions are members of a consortium set up in 2000 to allow economies of scale in the development, manufacture and purchasing of these filters.

The University of Reading are responsible for the spectral design and fabrication of the N-band (10.3 to 13.1 µm) and Q-band (16.5 - 24.5 µm) filters.

Delivered hardware

Description  Filter Type Quantity  Wavelength Region Substrate Material Dimensions 
N-Band Narrow Bandpass filters 12 channels 10.3 - 13.1 µm Zinc Sulphide (ZnS) 25.4 mm Dia x 3.7 mm T
Q-Band Narrow Bandpass filters 8 channels 16.5 - 24.5 µm Cadmium Telluride (CdTe), Zinc Selenide (ZnSe) 25.4 mm Dia x 3.7 mm T



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