1 August 2016 Characterizing the cross dispersion reflection gratings of CRIRES+
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Abstract
The CRIRES+ project attempts to upgrade the CRIRES instrument into a cross dispersed Echelle spectrograph with a simultaneous recording of 8-10 diffraction orders. In order to transform the CRIRES spectrograph into a cross-dispersing instrument, a set of six reflection gratings, each one optimized for one of the wavelength bands CRIRES+ will operate in (YJHKLM), will be used as cross dispersion elements in CRIRES+. Due to the upgrade nature of the project, the choice of gratings depends on the fixed geometry of the instrument. Thus, custom made gratings would be required to achieve the ambitious design goals. Custom made gratings have the disadvantage, though, that they come at an extraordinary price and with lead times of more than 12 months. To mitigate this, a set of off-the-shelf gratings was obtained which had grating parameters very close to the ones being identified as optimal. To ensure that the rigorous specifications for CRIRES+ will be fulfilled, the CRIRES+ team started a collaboration with the Physikalisch-Technische Bundesanstalt Berlin (PTB) to characterize gratings underconditions similar to the operating conditions in CRIRES+ (angle of incidence, wavelength range).

The respective test setup was designed in collaboration between PTB and the CRIRES+ consortium. The PTB provided optical radiation sources and calibrated detectors for each wavelength range. With this setup, it is possible to measure the absolute efficiency of the gratings both wavelength dependent and polarization state dependent in a wavelength range from 0.9 μm to 6 μm.
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Roman Follert, Dieter Taubert, Jörg Hollandt, Christian Monte, Ernesto Oliva, Ulf Seemann, Tom Löwinger, Heiko Anwand-Heerwart, Christof Schmidt, Reinhold J. Dorn, Paul Bristow, Artie Hatzes, Ansgar Reiners, Nikolai Piskunov, Ulrike Heiter, Eric Stempels, Thomas Marquart, Alexis Lavail, Claudio Cumani, Jason Grunhut, Andreas Haimerl, Renate Hinterschuster, Derek J. Ives, Yves Jung, Florian Kerber, Barbara Klein, Jean Louis Lizon, Ignacio Molina-Conde, Belinda Nicholson, Livia Origlia, Luca Pasquini, Jérôme Paufique, Jörg Stegmeier, Sebastien Tordo, "Characterizing the cross dispersion reflection gratings of CRIRES+", Proc. SPIE 9912, Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation II, 99122B (1 August 2016); doi: 10.1117/12.2232569; https://doi.org/10.1117/12.2232569
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