Speaker
Description
The impact on Virgo Sensitivity of the unwanted amplitude modulation of the Virgo Laser beam introduced as a collateral effect of its phase modulation, required by the adoption of the Pound-Drever-Hall technique, has been estimated at the end of O3 in preparation for the next Science Run. Its contribution turned out to be significative, reducing up to one third the target Sensitivity. That pushed for the development of a dedicated servo loop with the goal of reducing these variations to values of the order of few parts per billion of the amplitude of the required RF modulation lines adopted.
The Residual Amplitude Modulation Stabilization (RAMS) servo has been designed, built, installed, and commissioned before the beginning of the O4b data taking. Its measured suppression performances on the field are consistent with the design requirements. Further developments are planned for the future to include additional diagnostic features and improve system reliability and dynamics.