Missions

The EUCLID space telescope, launched in July 2023, consists of two instruments: one operating in the visible domain (VIS) and the other in the infrared domain (NISP). A dichroic beam splitter is used to separate the two measurement paths. It is positioned in the optical path of the EUCLID Korsch telescope after the M3 mirror, at the telescope's exit pupil. This component divides the incoming optical beam between the VIS and NISP spectral domains, providing distinct focal planes for each. It has been discovered that understanding the variation of the Wavefront Figure Error (WFE) introduced by this component across the entire visible observation band [550-900] nm is crucial for the project. Indeed, simulations have shown that phase variations in reflection (visible spectrum) exhibit abrupt changes at certain wavelengths, which affect the measurement of galaxy shapes.
A dedicated metrology bench has been funded and developed to precisely characterize the dependence of the WFE on wavelength, incidence angle, and polarization, enabling its modeling and removal from observed images. This work will be carried out on the twin dichroic mirror, which was manufactured at the same time as the one installed in the telescope. An innovative measurement method, called the PSF path, has been implemented in addition to the traditional Shack-Hartmann wavefront sensor measurement. This method is based on phase diversity techniques, where a camera images the beam around the focal point by inducing a known and controlled defocus. This complementary and independent measurement will help cross-validate the Shack-Hartmann sensor results. The objective of this work is to characterize and optimize the PSF path to provide an initial assessment of its performance and, if necessary, compare it with existing Shack-Hartmann measurements.

Activités

• Characterization of the PSF path of the OBSERVE metrology bench
• Optimization of the phase diversity measurement protocol
• Implementation of phase reconstruction algorithms
The post-doc will also participate in the progress meetings and in defining the test campaigns.

Compétences

• Expertise in high-precision optical measurements
• Mastery of Zernike polynomial decompositions
• Ability to critically analyze measurement series, identify and correct sources of error
• Programming skills in Matlab/Python
• Strong analytical and reporting skills
Experience in wavefront measurement would be highly appreciated. Autonomy and rigor will be essential for the successful completion of this activity.

Contexte de travail

The LMA platform of IP2I (UMR5822) specializes in the production and characterization of high-performance, large-dimension optics. Notably, it has produced all cavity mirrors for currently operating gravitational wave detectors (LIGO, Virgo, and KAGRA). Since 2018, the platform has been involved in the characterization of Euclid's dichroic beam splitter, a key element of the telescope, whose impact on performance affects the scientific objectives of the mission. A dedicated metrology bench, specially developed for this purpose by an industrial partner, has been installed and in operation since July 2023.
The LMA platform is organized into two departments (Thin Films and Metrology), comprising about a dozen engineers and technicians. It is part of IP2I, a joint research unit of CNRS and Université Lyon 1, focusing on research in particle physics, cosmology, and interdisciplinary applications.
Job Location
LMA Platform
Virgo Building
7 avenue Pierre de Coubertin
69100 Villeurbanne, France
The platform is a Restricted Regime Zone, and the candidate's arrival must be authorized by the CNRS Defense Security Officer (FSD).

Contraintes et risques

• Work in an ISO3 clean room environment
• Laser radiation in the work environment