Opto-mechanical design of a DMD multislit spectrograph for the ESA Euclid Mission

The Euclid mission proposed in the context of the ESA Cosmic Vision program is aimed to study the challenging problem of the Dark Energy, responsible of the acceleration of the Universe. One of the three probes of Euclid is dedicated to study the Baryonic Acoustic Oscillations by means of spectroscopic observations of millions of galaxies in the Near Infrared. One option for the Euclid Near Infrared Spectrograph (ENIS) is a multi-slit approach based on Digital Micromirror Device (DMD) used as reconfigurable slit mask. The Texas Instrument 2048*1080 DMD with 13.68 micrometers pitch has been chosen. ENIS optical design is composed of four arms each using one DMD to cover a total FOV of 0.48 square degree. The fore-optic design has to cope with the difficult task of having simultaneously a fast beam (F/2.7) and a quasi-diffraction limited image on a 24 deg tilted plane. The compact three mirrors spectrograph is using a grism in convergent beam for simplicity and compactness purposes. From the optical design, the mechanical structure is based on a common carbon honeycomb bench to reach the challenging requirements of volume and mass.