Image Slicer Performances from a Demonstrator for the SNAP/JDEM Mission, Part I: Wavelength Accuracy

A space-adapted visible and infrared spectrograph has been developed for the SNAP (SuperNova/Acceleration Probe) experiment proposed for JDEM. The instrument should have a high sensitivity to see faint supernovae, but also a good redshift determination better than 0.003(1 + z), and a precise spectrophotometry (2%). An instrument based on an integral-field method with the powerful concept of imager slicing has been designed. A large prototyping effort has been performed in France that validates the concept. In particular, a demonstrator reproducing the full optical configuration has been built and tested to prove the optical performance both in the visible and in the near-infrared range. This article, the first of two, focuses on wavelength measurement, while the second article will report on spectrophotometric performance. We address here the spectral accuracy expected both in the visible and in the near-infrared range in such a configuration, and we demonstrate, in particular, that the image slicer enhances the instrumental performances in the spectral measurement precision by removing the slit effect. This work is supported in France by CNRS/INSU/IN2P3 and by the French space agency (CNES), and in the US by the University of California.