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Abstract

The Euclid payload features two instruments that are observing the sky simultaneously. The visual light high spatial resolution imager (VIS) and the Near Infrared Spectrometer and Photometer (NISP). A Korsch type telescope with 1,2m diameter feeds both instruments via a dichroic beamsplitter. The NISP instrument reduces the incoming f/#20 beam of the telescope to an f/# 10 beam. The instruments optical system, the NISP Optical Assembly (NI-OA) contains 4 lenses, one single lens in front of a Grism and Filter wheel which is called collimator lens assembly (CoLA), and a lens triplet between these Grism and Filter wheel and the instruments focal plane, which is called camera lens assembly (CaLA). The focal plane consists of 16 Hawaii 2RG detectors.

The required alignment accuracy of the lens triplet and of the singlet relative to the triplet is very demanding and needs to be achieved and verified at the operational temperature of 134K. As an introduction the design, the integration and alignment concept are briefly summarized, as well as the measurement concept to verify the cold alignment within the cryostat. Alignment results for the integration of CaLA EQM and FM at room temperature are presented, the alignment stability after vibrational loads and thermal vacuum cycling is high, only minor changes of a few μm and arcsecs can be detected. The accuracy of the measured cryogenic alignment is demonstrated to be just a few μm and arcsec off the ideal predicted opto-mechanical alignment.