24 July 2014 Integration and testing of the GRAVITY infrared camera for multiple telescope optical beam analysis
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Abstract
The GRAVITY Acquisition Camera was designed to monitor and evaluate the optical beam properties of the four ESO/VLT telescopes simultaneously. The data is used as part of the GRAVITY beam stabilization strategy. Internally the Acquisition Camera has four channels each with: several relay mirrors, imaging lens, H-band filter, a single custom made silica bulk optics (i.e. Beam Analyzer) and an IR detector (HAWAII2-RG). The camera operates in vacuum with operational temperature of: 240k for the folding optics and enclosure, 100K for the Beam Analyzer optics and 80K for the detector. The beam analysis is carried out by the Beam Analyzer, which is a compact assembly of fused silica prisms and lenses that are glued together into a single optical block. The beam analyzer handles the four telescope beams and splits the light from the field mode into the pupil imager, the aberration sensor and the pupil tracker modes. The complex optical alignment and focusing was carried out first at room temperature with visible light, using an optical theodolite/alignment telescope, cross hairs, beam splitter mirrors and optical path compensator. The alignment was validated at cryogenic temperatures. High Strehl ratios were achieved at the first cooldown. In the paper we present the Acquisition Camera as manufactured, focusing key sub-systems and key technical challenges, the room temperature (with visible light) alignment and first IR images acquired in cryogenic operation.
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Paulo Gordo, Antonio Amorim, Jorge Abreu, Frank Eisenhauer, Narsireddy Anugu, Paulo Garcia, Oliver Pfuhl, Marcus Haug, Eckhard Sturm, Ekkehard Wieprecht, Guy Perrin, Wolfgang Brandner, Christian Straubmeier, Karine Perraut, M. Duarte Naia, M. Guimarães, "Integration and testing of the GRAVITY infrared camera for multiple telescope optical beam analysis", Proc. SPIE 9146, Optical and Infrared Interferometry IV, 91461V (24 July 2014); doi: 10.1117/12.2056572; https://doi.org/10.1117/12.2056572
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