ANDES, the high-resolution spectrograph for the ELT: stray light analysis of the RIZ spectrograph preliminary optical design

Le résumé fourni par la source

ANDES (ArmazoNes high Dispersion Echelle Spectrograph) is one of the first-generation instruments of the ELT. It is an optical-infrared high-resolution spectrograph (R = 100 000) covering 0.4–1.8 µm in baseline, with extensions in the U and K bands as goals. The RIZ spectrograph, under the responsibility of the University of Geneva, addresses the 623–950 nm wavelength range. Following the preliminary optical design of the RIZ spectrograph already presented at SPIE 2024 [1], this paper focuses on the straylight analysis of that design. After briefly recalling the optical architecture, we describe the methodology and tools used to assess ghost contributions, the dedicated mitigation features included in the design (wedged Mangin field mirror, wedged dichroic beam splitter and cross-disperser prisms, baffling strategy), and the analysis at element level and at full-system level performed in TracePro©. We show that the most significant ghost contributors are the back-reflection of the detector onto the last camera lens. On top of that the IZ band is affected by “focussed slit images” due to internal reflections inside the cross-disperser and beam splitter prisms, and round trip from the detector to the slit assembly. The maximum peak ghost intensity reaches the upper limit of 0.1 %, allowed by the requirement.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.