Opto-mechanical design of ShaneAO: the adaptive optics system for the 3-meter Shane Telescope

Abstract

A Cassegrain mounted adaptive optics instrument presents unique challenges for opto-mechanical design. The flexure and temperature tolerances for stability are tighter than those of seeing limited instruments. This criteria requires particular attention to material properties and mounting techniques. This paper addresses the mechanical designs developed to meet the optical functional requirements. One of the key considerations was to have gravitational deformations, which vary with telescope orientation, stay within the optical error budget, or ensure that we can compensate with a steering mirror by maintaining predictable elastic behavior. Here we look at several cases where deformation is predicted with finite element analysis and Hertzian deformation analysis and also tested. Techniques used to address thermal deformation compensation without the use of low CTE materials will also be discussed.

Preliminary lab demonstration of a 3-sided reflective pyramid wavefront sensor for Shane AO using SEAL testbed

“…4. 4 This mechanical configuration is the motivation behind the 3-RPWFS optical design; the Shane AO module and OTA does not easily allow for a fully reflective system.…”

ShaneAO: wide science spectrum adaptive optics system for the Lick Observatory

“…Key optical mounts are designed particularly stiff and the optical bench is held in a stress-free manner. 3 The structure is designed to keep the nominal mechanical drift low and elastically repeatable so a flexure compensation model can take over to reach the final goal.…”

Swimming with ShARCS: comparison of on-sky sensitivity with model predictions for ShaneAO on the Lick Observatory 3-meter telescope

“…• A new support structure for the AO system and camera designed to reduce flexure and improve longexposure stability. 8 The assembly is also designed to be rotated with precision to allow for long-exposure, long-slit spectroscopy.…”