Experimental investigation of stray light from dust contamination in gravitational wave detectors

Stray light presents a significant challenge in the LIGO-Virgo interferometers, manifesting as excess noise in the low-frequency region and causing a loss in sensitivity both through increased measurement noise and disruption of control loops. This issue is expected to be even more critical in future interferometers, such as the Einstein Telescope (ET), which will have higher sensitivity in the low-frequency region. Therefore, effective monitoring and mitigation of stray light sources are crucial. This thesis focuses on understanding and controlling stray light contributions, primarily from surface roughness and dust particles deposited on optical components. The Bidirectional Scattering Distribution Function (BSDF) and Total Integrated Scattering (TIS) are utilized to model and characterize stray light sources. The Harvey-Shack model and its generalized form, along with Mie scattering theory, are applied to understand the scattering phenomena. The research included significant enhancements to a scattering measurement facility, including background noise optimization and the implementation of automated measurement procedures. Various samples, including baffle components from Virgo detectors, absorbent glass samples, and silicon wafers used in dust monitoring campaigns, were characterized using the improved facility for their scattering properties. The facility's future focus will be on supporting the dust monitoring campaign, with new wafers periodically exposed in various environments of the Virgo laboratories to monitor dust accumulation. These measurements will help validate BSDF estimates and improve the overall understanding of stray light contributions in gravitational wave detectors.