Speaker
Description
Scattered light that re-couples with the main beam of current gravitational wave detectors is a major limitation of their sensitivity, particularly at low frequencies. The detector noise depends on the amount of produced scattered light and the relative motion between the scattering objects and the interferometer. To address this issue in Virgo, we estimated the amount of scattered light generated by the most critical objects on the suspended benches (i.e. OFI, OMC, photodiodes etc), either measuring it with a back-scatterometer at LAPP or computing it. Then, we derived the scattered light noise projections for all the Virgo suspended benches. The projections were compared to the measurements from O3 and O4 and showed a reduction of scattered light due to the mitigation campaign carried out during the commissioning for O4. Additionally, we measured the scattered light noise coming from the critical elements in LIGO Hanford to estimate the amount of re-coupled light, including the one coming from the squeezing port. The results of this study allow to better understand the current limitations and to take actions for the future upgrades of gravitational waves detectors.
