Light Scattering from Dust Contamination in Gravitational-Wave Interferometric Detectors

The aim of this thesis is to study the stray light contribution from dust particles in the environments of the gravitational-wave (GW) Interferometer (ITF). Stray light manifests as an excess noise in the low-frequency range of the ITF, limiting the sensitivity and our ability to detect low-frequency signals. Along surface roughness, dust contamination on optics, even in the clean room environments of the ITF, can significantly contribute to stray light. To measure the dust contamination in Virgo, we expose clean silica wafers as witness samples in the Quantum Noise Reduction (QNR) and Clean Room environments. The samples are exposed in different conditions and are photographed with a custom camera system. To analyze the photos we use a Matlab algorithm to count the dust particles deposited and reconstruct their dimensions. We present the upgrades and improvements that we have performed on the algorithm. We then analyse the samples, and from the reconstructed distributions present how cleanliness levels are used to monitor the environments and to estimate the stray light contributed by dust accumulation on optics.