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Mode sensing with the phase camera for gravitational-wave interferometers by Ricardo de ABREU SILVERIO CABRITA -
Lundi 12 janvier 2026 à 15h30 - Auditoire CYCL01 - Bâtiment de Hemptinne - Chemin du Cyclotron, 2 - 1348 Louvain-la-Neuve -
Gravitational-wave (GW) interferometers have detected over two hundred compact binary coalescences to date. This was achieved with long-baseline Michelson interferometers that employ hundreds of kWs of optical power circulating in km-long optical cavities. In addition, squeezed light is injected into the interferometer in order to beat the standard quantum noise limit.
Optical absorption in the optics leads to thermal effects that shift the eigenmodes of the optical cavities, causing control issues. This shift also leads to mode mismatch which results in optical losses. In addition, high-power effects such as parametric instabilities make the operation of optical cavities with high-circulating power notoriously difficult.
In turn, quantum noise reduction techniques are sensitive to optical losses and mode degradation. The combination of high-power with squeezed light makes mode sensing and control a crucial aspect of operating a gravitational-wave interferometer. This is particularly the case for next-generation detectors, for which some of the major planned upgrades include increasing circulating powers to the MW level and increase quantum noise reduction up to 10dB.
In this work, we use a spatio-temporal heterodyne wavefront sensor to tackle these challenges. This sensor is called the phase camera and is currently installed at the Virgo GW detector. It combines a heterodyne readout with beam scanning to achieve high-resolution amplitude and phase images of the laser beam wavefront.
This work is divided in two parts. One concerns the phase cameras of Virgo, their use for optical characterization as well as optical simulations of the Virgo detector. The second consists of two-table top experiments with a custom phase camera. In these, two novel mode sensing schemes are demonstrated that should help achieve the high-power goals of future GW detectors.
Jury members :
Prof. Prof. Clément Lauzin (UCLouvain) (Supervisor)
Prof. Prof. Giacomo Bruno (UCLouvain) (Supervisor)
Prof. Prof. Joris van Heijningen (VU Amsterdam) (Supervisor)
Dr. Andrea Giammanco (UCLouvain) (Chairperson)
Prof. Prof. Matthieu Génévriez (UCLouvain) (Secretary)
Dr. Matteo Tacca (Nikhef, Amsterdam)
Dr. Jérôme Degallaix (IP2I-Lyon)
Pay attention : the public defense of Ricardo de ABREU SILVERIO CABRITA will also take place in the form of a videoconference
