Laser-interferometer gravitational-wave optical-spring detectors

TL;DR

This paper models the quantum mechanical behavior of LIGO-like gravitational-wave detectors, revealing an optical spring effect that alters mirror dynamics and impacts noise reduction strategies, but introduces stability challenges.

Contribution

It introduces a quantum mechanical framework for understanding optical springs in gravitational-wave detectors, highlighting their effects on mirror dynamics and noise optimization.

Findings

Optical springs cause mirrors to respond as if attached to a spring.

The system exhibits dynamic instability requiring control systems.

Enhanced understanding of noise curve reshaping possibilities.

Abstract

Using a quantum mechanical approach, we show that in a gravitational-wave interferometer composed of arm cavities and a signal recycling cavity, e.g., the LIGO-II configuration, the radiation-pressure force acting on the mirrors not only disturbs the motion of the free masses randomly due to quantum fluctuations, but also and more fundamentally, makes them respond to forces as though they were connected to an (optical) spring with a specific rigidity. This oscillatory response gives rise to a much richer dynamics than previously known, which enhances the possibilities for reshaping the LIGO-II's noise curves. However, the optical-mechanical system is dynamically unstable and an appropriate control system must be introduced to quench the instability.