Double optical spring enhancement for gravitational wave detectors

TL;DR

This paper proposes a novel double optical spring scheme for gravitational wave detectors, enhancing sensitivity and stability by trapping test masses with two light fields, and offers flexible noise shaping for targeted source detection.

Contribution

It introduces an all-optical stabilization method using two optical springs, providing improved control and noise optimization over traditional feedback systems.

Findings

Enhanced stability of test masses through double optical springs

Flexible noise spectral density re-shaping capabilities

Potential for further optimization with multi-spring systems

Abstract

Currently planned second-generation gravitational-wave laser interferometers such as Advanced LIGO exploit the extensively investigated signal-recycling (SR) technique. Candidate Advanced LIGO configurations are usually designed to have two resonances within the detection band, around which the sensitivity is enhanced: a stable optical resonance and an unstable optomechanical resonance - which is upshifted from the pendulum frequency due to the so-called optical-spring effect. Alternative to a feedback control system, we propose an all-optical stabilization scheme, in which a second optical spring is employed, and the test mass is trapped by a stable ponderomotive potential well induced by two carrier light fields whose detunings have opposite signs. The double optical spring also brings additional flexibility in re-shaping the noise spectral density and optimizing toward specific gravitational-wave sources. The presented scheme can be extended easily to a multi-optical-spring system that allows further optimization.