Testing the near-infrared optical assembly of the space telescope Euclid

TL;DR

This paper evaluates the optical assembly of the Euclid space telescope, demonstrating diffraction-limited imaging performance across its wide field of view through wavefront measurements and simulations under space-like conditions.

Contribution

It provides the first comprehensive testing and validation of Euclid's near-infrared optical assembly's imaging quality in space-like conditions, using multiple measurement techniques.

Findings

Optical assembly achieves diffraction-limited performance across the entire field.

Wavefront measurements and simulations are in good agreement.

The assembly meets the stringent imaging quality requirements for Euclid.

Abstract

Euclid is a space telescope currently developed in the framework of the ESA Cosmic Vision 2015-2025 Program. It addresses fundamental cosmological questions related to dark matter and dark energy. The lens system of one of the two scientific key instruments [a combined near-infrared spectrometer and photometer (NISP)] was designed, built-up and tested at the Max Planck Institute for Extraterrestrial Physics (MPE). We present the final imaging quality of this diffraction-limited optical assembly with two complementary approaches, namely a point-spread function and a Shack-Hartmann sensor-based wavefront measurement. The tests are performed under space operating conditions within a cryostat. The large field of view of Euclid's wide-angle objective is sampled with a pivot arm, carrying a measurement telescope and the sensors. A sequence of highly accurate movements to several field positions is carried out by a large computer controlled hexapod. Both measurement approaches are compared among one another and with the corresponding simulations. They demonstrate in good agreement a solely diffraction limited optical performance over the entire field of view.