Resonant dampers for parametric instabilities in gravitational wave detectors

Abstract

Advanced gravitational wave interferometric detectors will operate at their design sensitivity with nearly $\ensuremath{\sim}1\text{ }\text{ }\mathrm{MW}$ of laser power stored in the arm cavities. Such large power may lead to the uncontrolled growth of acoustic modes in the test masses due to the transfer of optical energy to the mechanical modes of the arm cavity mirrors. These parametric instabilities have the potential to significantly compromise the detector performance and control. Here we present the design of ``acoustic mode dampers'' that use the piezoelectric effect to reduce the coupling of optical to mechanical energy. Experimental measurements carried on an Advanced LIGO-like test mass have shown a tenfold reduction in the amplitude of several mechanical modes, thus suggesting that this technique can greatly mitigate the impact of parametric instabilities in advanced detectors.