LIGO Seminar

Title: Scattered light in ground-based gravitational wave detectors: control and mitigation strategies

Adrian Macquet and Marc Andres

Location: West Bridge 351 and broadcasting over zoom at the usual link: https://caltech.zoom.us/j/82072539167

Abstract: Light that is scattered away from the main laser beam can be an important source of noise in gravitational wave detectors. As part of the design of the Einstein Telescope (ET), a thorough study of the scattered light and its impact in the sensitivity must therefore be performed. Here we present a preliminary estimation of the sources of scattered light inside the main arms of ET. We then propose a baffle configuration for ET as a recommendation during the design phase and an analytic estimation of the noise. The results point out that the scattered light noise can be sub-dominant at all frequencies, not limiting the sensitivity of the interferometer. In a second part, we present new instrumented baffles designed to provide real-time monitoring of the scattered light at low angles in the main arms of Virgo. A first instrumented baffle was installed in 2021 around the end mirror of the input mode cleaner at Virgo, and similar instruments will be installed around the end mirrors in the main arms before O5. In this context, we describe optical simulations of the light distribution in the detector's main cavities to assess the ability of the sensors to effectively monitor the mirror's surface and to detect the presence of point absorbers, as well as to detect potential misalignment and to play a role in the pre-alignment of the interferometer.