Electromagnetic Noise in Gravitational-Wave Detectors

The observation of gravitational waves represents the ultimate frontier of contemporary multi-messenger astronomy. This scientific milestone is achieved through long-baseline laser interferometers, complex instruments capable of detecting spacetime metric perturbations with a strain sensitivity on the order of 10^−22 (corresponding to test mass displacements of approximately 10^−18 m). Reaching such extreme precision requires highly sophisticated noise isolation and mitigation strategies. Among these noise sources, electromagnetic noise is playing an increasingly decisive role, emerging as a primary limiting factor for the low-frequency sensitivity of current and future thirdgeneration detectors. However, the research effort dedicated to this noise source has not kept pace with its growing phenomenological impact. This doctoral thesis develops a systematic treatment of electromagnetic noise, aiming to outline the current state of the art and, crucially, to identify the boundaries of our current understanding and mitigation capabilities. By integrating numerical modeling with experimental validation — including the development of the MANET facility and the investigation of advanced shielding and actuator redesign (CALMA project) — this work establishes the methodological foundations for a ’by-design’ management of magnetic noise, a fundamental prerequisite for the ultimate scientific success of the Einstein Telescope. Furthermore, by proposing an in-situ monitoring system, this work provides a framework for the investigation of electrostatic noise, addressing the current uncertainties regarding charge deposition on test masses.