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6 July 2018 Thermal and mechanical design and test of the CCD mount for the WEAVE spectrograph cryostats
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Abstract
WEAVE is the new multi-object spectrograph for the William Herschel Telescope on La Palma. The culmination of prime focus, the large number of fibers and the wide resolution range has required a stringent optical design, which in turn demands a spectrograph with tight positional tolerances and large final focal plane. To capture this focal plane each of the two cryostats has two e2v 6k × 6k CCDs mounted as a mosaic. As well as being cooled to 150K via liquid nitrogen, the positional tolerances for the sensitive areas are flatness 60μm p-v over the entire image area, rotation around X and Y axis ±50 arcmin, translation in X, Y and Z ± 50 micron. We have used a Stil confocal measuring head mounted on two Thorlab translation stages to create a X,Y mount, controlled by a Raspberry Pi that is capable of recording measurements in Z to better than 1μm accuracy. This is used to measure the flatness and deformation of the image area under vacuum, and when cooled to 150K and the overall tip and tilt of the image plane to ensure they meet specification and are repeatable. In addition to this measuring system, we use a Thorlabs CMOS camera with a Navitar 50mm lens to ensure each CCDs image area is within specification with regards X and Y translation. In order to satisfy the above requirements, we designed the CCD mount to be adjustable (on initial setup), correctly constrained, isolated from liquid nitrogen boil-off vibration, and thermally insulating.
© (2018) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Stuart D. Bates, Iain A. Steele, Chris J. Mottram, Helen E. Jermak, Niels Tromp, Jan Kragt, Eddy Elswijk, Johan Pragt, Remko Stuik, Robert Barnsley, Charles Monroe, Gavin Dalton, Scott Trager, Jose Alfonso Lopez Aguerri, Piercarlo Bonifacio, Antonella Vallenari, Esperanza Carrasco, Don Carlos Abrams, and Kevin Middleton "Thermal and mechanical design and test of the CCD mount for the WEAVE spectrograph cryostats", Proc. SPIE 10709, High Energy, Optical, and Infrared Detectors for Astronomy VIII, 107091Z (6 July 2018); https://doi.org/10.1117/12.2312496
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