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Sliding Optics

Submitter: Ramon Navarro
Description: Exciting times at NOVA-ASTRON these days. We are at the final stages of integration of the Cold Optical Bench for MATISSE; the mid-infrared interferometric spectrograph and imager for ESO's VLT interferometer (VLTI) at Paranal, Chile. Matisse can combine the light from all 4 eight-meter VLT telescopes.

In this picture you can see a detail of the photometric slider. This component either sends all the light towards the interferometric channel or splits of part of the light of each telescope for photometric detection. The first mode is for maximum sensitivity and uses gold coated mirrors (seen grey seen from behind in this picture). The second mode is for maximum accuracy and uses Zink-Selenide with a beam splitter coating on the entrance side and an anti-reflection coating on the exit side. The Zink Selenide must be relatively thick in order to spatially remove unwanted double reflections.

Alignment must be maintained while switching between modes and therefore the aluminum mounting surface for the optical components is lapped to optical tolerances (the shiny silver surface at the bottom of the image). This surface is also used for the bearings in order to minimize the tolerance train. On top of all optical components you see spring systems that keep the optics aligned under all circumstances; the operating temperature is 38 Kelvin and the VLTI is located in an earth quake zone.

MATISSE is capable of imaging at spatial resolutions of ~6 milli-arcsec in the 2.8-5 and 8-13 micrometer wavelength range. This enables the study of wavelength-dependent characteristics of gas and dust grains. This includes the formation and evolution of planetary systems, Active Galactic Nuclei and high-contrast environment of evolved stars.
Copyright: Ramon Navarro
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