M2 : Study of an optical light filtering system to improve the sensitivity of the Virgo gravitational-wave detector

The Virgo interferometer is made up of several optical cavities, so that photons travel an average of 1,000 km in each arm of the interferometer before forming the interference pattern. Furthermore, as the photons are recycled, they are reflected off the mirrors tens of thousands of times. In these conditions, even if the mirrors are close to perfect, some of the light is scattered onto higher-order modes, making the interference imperfect and reducing the instrument’s signal-to-noise ratio. To reduce these effects, an optical cavity, known as a “mode-cleaner”, is used at the output of the interferometer to filter the beam. The subject of this internship is this optical filtering system, and will be developed in two ways. Firstly, we plan to change the design of this cavity from a monolithic glass cavity to one composed of several mirrors. This change should make it possible to reduce thermal effects in this cavity and cut its optical losses. In parallel, we plan to add other optical cavities to the other beams coming from the interferometer, to improve the quality of the signals extracted from those beams which are used to control the interferometer. The student will participate in the design and testing of these systems. Part of this work will take place in the Virgo/LAPP group’s optics laboratory.

Possible indication of an opening towards a thesis subject: : This internship is intended to lead to a thesis. Indeed, this work will lead to the improvement of the detector whose installation is due to start in 2025.