22 July 2008 VIRUS-P: camera design and performance
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Abstract
We present the design and performance of the prototype Visible Integral-field Replicable Unit Spectrograph (VIRUS-P) camera. Commissioned in 2007, VIRUS-P is the prototype for 150+ identical fiber-fed integral field spectrographs for the Hobby-Eberly Telescope Dark Energy Experiment. With minimal complexity, the gimbal mounted, double-Schmidt design achieves high on-sky throughput, image quality, contrast, and stability with novel optics, coatings, baffling, and minimization of obscuration. The system corrector working for both the collimator and f / 1.33 vacuum Schmidt camera serves as the cryostat window while a 49 mm square aspheric field flattener sets the central obscuration. The mount, electronics, and cooling of the 2k × 2k, Fairchild Imaging CCD3041-BI fit in the field-flattener footprint. Ultra-black knife edge baffles at the corrector, spider, and adjustable mirror, and a detector mask, match the optical footprints at each location and help maximize the 94% contrast between 245 spectra. An optimally stiff and light symmetric four vane stainless steel spider supports the CCD which is thermally isolated with an equally stiff Ultem-1000 structure. The detector/field flattener spacing is maintained to 1 μm for all camera orientations and repeatably reassembled to 12 μm. Invar rods in tension hold the camera focus to ±4 μm over a -5-25 °C temperature range. Delivering a read noise of 4.2 e- RMS, sCTE of 1-10-5 , and pCTE of 1-10-6 at 100 kpix/s, the McDonald V2 controller also helps to achieve a 38 hr hold time with 3 L of LN2 while maintaining the detector temperature setpoint to 150 μK (5σ RMS).
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Joseph R. Tufts, Phillip J. MacQueen, Michael P. Smith, Pedro R. Segura, Gary J. Hill, Robert D. Edmonston, "VIRUS-P: camera design and performance", Proc. SPIE 7021, High Energy, Optical, and Infrared Detectors for Astronomy III, 702109 (22 July 2008); doi: 10.1117/12.790099; https://doi.org/10.1117/12.790099
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