First Demonstration of Electrostatic Damping of Parametric Instability at Advanced LIGO

TL;DR

This paper demonstrates the first active electrostatic damping of a parametric instability in an advanced LIGO interferometer, showing effective suppression of mirror acoustic modes to improve high-power operation.

Contribution

It introduces a novel active feedback technique using electrostatic actuation to damp parametric instabilities in gravitational wave detectors.

Findings

Successfully damped a 15,538 Hz mode with a decay time of 23 sec

Damped an exponential growth mode with a 182 sec time constant

Achieved stabilization with an average control force of 0.03 nNrms

Abstract

Interferometric gravitational wave detectors operate with high optical power in their arms in order to achieve high shot-noise limited strain sensitivity. A significant limitation to increasing the optical power is the phenomenon of three-mode parametric instabilities, in which the laser field in the arm cavities is scattered into higher order optical modes by acoustic modes of the cavity mirrors. The optical modes can further drive the acoustic modes via radiation pressure, potentially producing an exponential buildup. One proposed technique to stabilize parametric instability is active damping of acoustic modes. We report here the first demonstration of damping a parametrically unstable mode using active feedback forces on the cavity mirror. A 15,538 Hz mode that grew exponentially with a time constant of 182 sec was damped using electro-static actuation, with a resulting decay time constant of 23 sec. An average control force of 0.03 nNrms was required to maintain the acoustic mode at its minimum amplitude.