Charlotte Bragard, Giacomo Bruno, Ricardo Cabrita, Pavel Demin, Swapnil Dhage, Rodney Eckler, Vito Garzone, Aaron Goodwin-Jones, Alexander Moncello, Nicolas Szilasi, Morgane Zeoli, Jue Zhang

Gravitational wave detectors based on Michelson interferometry (such as LIGO, Virgo, ET) use very high laser powers and quantum-optics to overcome fundamental noises associated with the Heisenberg Uncertainty Principle. However, these high optical powers present a number of challenges including:
- Themoelastically driven changes in the mirror radii of curvature. This leads to:
+ Reduced optical power, therefore reduced sensitivity,
+ Modifications to the phase of optical control fields, limiting the operational time and power of the detectors
+ Quantum hyperloss, leading to reduced sensitivity
- Parametric instability - an optomechanical coupling that degrades interferometer sensitivity
- Angular instability, such as siggs-sidles.

ET-OPT is a next-generation high-power interferometry platform being developed at UCLouvain to advance optical technologies for future gravitational-wave observatories such as the Einstein Telescope and Virgo. The project focuses on developing real-time optical mode control loops in a prototype scale infrastructure. This unlocks the following possibilities:
- Increase optical power in today's gravitational wave detectors (such as Virgo)
- A concrete route towards the 3 MW of optical power targeted by ET
- New possibilities, such as the use of higher order modes for coating brownian noise reduction
- Dynamic control of gouy phase, without causing hyperloss, thus facilitating PI suppression

The work is carried out in close collaboration with Virgo and ET scientific consortia.

External collaborators: Nicolas Letendre (Laboratoire d'Annecy de Physique des Particules), Alain Masserot (Laboratoire d'Annecy de Physique des Particules), Emmanuel Pacaud (Laboratoire d'Annecy de Physique des Particules), Carl Blair (University of Western Australia), Haochen Zhu (University of Western Australia), Chunnong Zhao (University of Western Australia), Liu Jian (University of Western Australia), Christophe Collette (ULiege), Matteo Tacca (Nikhef), Martin van Beuzekom (Nikhef), Sebastian Steinlechner (ETpf), André Füzfa (UNamur).