Liger at Keck Observatory: Design of Imager Optical Assembly and Spectrograph Re-Imaging Optics

TL;DR

This paper details the design and analysis of the optical assembly for Liger, an adaptive optics fed imager and spectrograph at Keck Observatory, including innovative alignment and baffling techniques.

Contribution

It introduces the design and assembly process of the Liger optical system, including the spectrograph RIO and alignment methods, tailored for cryogenic operation.

Findings

Optical components are assembled and aligned on a single plate.

Baffling effectively suppresses background and scattered light.

System will be characterized in a cryogenic test chamber.

Abstract

Liger is an adaptive optics (AO) fed imager and integral field spectrograph (IFS) designed to take advantage of the Keck All-sky Precision Adaptive-optics (KAPA) upgrade for the W.M. Keck Observatory. We present the design and analysis of the imager optical assembly including the spectrograph Re-Imaging Optics (RIO) which transfers the beam path from the imager focal plane to the IFS slicer module and lenslet array. Each imager component and the first two RIO mechanisms are assembled and individually aligned on the same optical plate. Baffling suppresses background radiation and scattered light, and a pupil viewing camera allows the imager detector to focus on an image of the telescope pupil. The optical plate mounts on an adapter frame for alignment of the overall system. The imager and RIO will be characterized in a cryogenic test chamber before installation in the final science cryostat.