A Precision Cryogenic Positioning Stage for Detector Dithering and Flexure Compensation

TL;DR

This paper details the design and initial performance of a cryogenic X-Y stage for detector dithering and flexure compensation in a large infrared spectrograph, enhancing image stability and sampling accuracy.

Contribution

It introduces a novel cryogenic piezo-driven stage with magnetoresistive feedback for improved detector positioning in astronomical instruments.

Findings

High-resolution, backlash-free motion achieved at 120 K

Effective flexure compensation using lookup table control

Prototype demonstrates promising accuracy and stability

Abstract

This paper presents the design and technical progress of a precision X-Y stage for detector dithering and flexure compensation. The stage is being developed for use in the Magellan InfraRed Multi-Object Spectrograph, MIRMOS. MIRMOS is a very large Nasmyth mounted spectrograph containing a combination of refractive, reflective and diffractive optics mounted on a long cryogenic optical bench. The instrument utilizes five science cameras, each having a custom x-y stage to control the in-plane detector position within each camera, providing both dithering capability for improved sampling, and flexure compensation to correct for image motion that results from the gravity variant operation of the instrument. Designed to operate at 120~K, the stage will accurately control detector position in two orthogonal degrees of freedom, and have manual fine adjustment features to set detector tip, tilt and piston. The piezo-driven flexure stage provides high-resolution backlash-free motion of the detector and is very compact along the optical path, keeping camera length to a minimum. A magnetoresistive bridge provides position feedback in each degree of freedom, greatly reducing hysteresis, which is common in piezoelectric actuators. The system is designed to operate in open loop using a lookup table keyed to the Nasmyth rotator angle for flexure control. Here, the optomechanical design of the stage, electrical control system, and current performance results from early prototype efforts are presented and discussed.