The MICADO Atmospheric Dispersion Corrector: Optomechanical design, expected performance and calibration techniques

TL;DR

This paper discusses the design, expected performance, and calibration techniques of the MICADO atmospheric dispersion corrector for the ELT, aiming to improve infrared image quality by reducing atmospheric dispersion effects.

Contribution

It presents the optomechanical design and calibration plan for a cryogenic ADC using Amici prisms for the ELT's MICADO instrument, highlighting innovations in performance and calibration methods.

Findings

ADC reduces atmospheric dispersion below 2.5 mas

Cryogenic environment impacts performance considerations

Calibration plan involves diffraction mask in cold pupil

Abstract

The differential refraction of light passing through the atmosphere can have a severe impact on image quality if no atmospheric dispersion corrector (ADC) is used. For the Extremely Large Telescope (ELT) this holds true well into the infrared. MICADO, the near-infrared imaging camera for the ELT, will employ a cryogenic ADC consisting of two counter-rotating Amici prisms with diameters of 125 mm. The mechanism will reduce the atmospheric dispersion to below 2.5 milli arcseconds (mas), with a set goal of 1 mas. In this report, we provide an overview of the current status of the ADC in development for MICADO. We summarise the optomechanical design and discuss how the cryogenic environment impacts the performance. We will also discuss our plan to use a diffraction mask in the cold pupil to calibrate and validate the performance once the instrument is fully integrated.