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In this article the immersed gratings for the ESA Copernicus Sentinel-5 mission are presented. The manufacturing approach is shown and the optical performance of the SWIR-3 immersed gratings as well as the results of the environmental tests are discussed. The immersed gratings show an average efficiency of 60% and a wavefront error of 200 nm rms. The total integrated scatter over the complete stray-light hemisphere excluding ghosts from internal reflections is found to be 0.2% using a conservative estimate. A method for the derivation of the wavefront error from separate surface measurements is presented and the results are compared to measurements with an experimental Shack- Hartmann setup. The immersed gratings are produced by bonding a prism to a wafer with a grating. Environmental tests and testing at operational temperatures show the suitability of this approach for complex space optical components. The article concludes with possible improvements in the optical performance of future immersed gratings.

In the context of the SAFARI instrument (SpicA FAR-infrared Instrument) SRON is developing a test environment to verify the SAFARI performance. The characterization of the detector focal plane will be performed with a back-illuminated pinhole over a reimaged SAFARI focal plane by an XYZ scanning mechanism that consists of three linear stages stacked together. In order to reduce background radiation that can couple into the high sensitivity cryogenic detectors (goal NEP of 2·10 -19 W/¥ Hz and saturation power of few femtoWatts) the scanner is mounted inside the cryostat in the 4K environment. The required readout accuracy is 3 µm and reproducibility of 1 µm along the total travel of 32 mm. The stage will be operated in “on the fly” mode to prevent vibrations of the scanner mechanism and will move with a constant speed varying from 60 µm/s to 400 µm/s. In order to meet the requirements of large stroke, low dissipation (low friction) and high accuracy a DC motor plus spindle stage solution has been chosen. In this paper we will present the stage design and stage characterization, describing also the measurements setup. The room temperature performance has been measured with a 3D measuring machine cross calibrated with a laser interferometer and a 2-axis tilt sensor. The low temperature veri fication has been performed in a wet 4K cryostat using a laser interferometer for measuring the linear displacements and a theodolite for measuring the angular displacements. The angular displacements can be calibra ted with a precision of 4 arcsec and the position could be determined with high accuracy. The presence of friction caused hgher values of torque than predicted and consequently higher dissipation. The thermal model of the stage ha s also been verified at 4K. Keywords: cryo-mechanism, bearings, linear stage, DC motor