The thesis will be carried out in the Institut Fresnel's CONCEPT team. The person recruited will benefit from the scientific and material support of the team and the associated platform (DIFFUSIF). Part of the experimental work will be carried out in a clean room.

Gravitational astronomy (Nobel Prize 2017) is enjoying considerable growth thanks to the unique performance of giant interferometers operating with arms of the order of a kilometre (Virgo/LIGO/KAGRA). New instruments are being developed to extend our observation of the universe even further, both on Earth (Einstein Telescop, Advanced Virgo in Europe and Cosmic Explorer in the USA) and in space (LISA, Europe and USA). The progress achieved has enabled us to move from detecting one gravitational event per month (2016) to one event per week (2019), and this rate of occurrence is expected to be extended to one event per minute by 2035 (terrestrial systems), or even to a continuum of observations with the LISA space project.
All these systems are based on interferometers with large arms ranging in size from 3 to 40 km for terrestrial interferometers. Their sensitivity to the passage of gravitational waves is intrinsically linked to the quality of the mirrors that form these giant cavities. Since the optical losses required must be less than ppm, it is vital to have reliable metrology resources that can measure very low losses, including scattering and absorption.
The core of this thesis will be the development of a device that will enable a complete assessment of optical losses, including their location and discrimination between scattering and absorption.
This work will be carried out within the Institut Fresnel's CONCEPT team, which is an expert in the development of instrumentation for the optical metrology of very low fluxes, and in close interaction with the Virgo Collaboration, which will also exploit the results.
Key words : Physics, Optics, instrumentation, metrology, optical components