Readout and Control of a Power-recycled Interferometric Gravitational-wave Antenna

TL;DR

This paper details the design and implementation of the readout and control systems for LIGO's interferometric gravitational wave detector, focusing on maintaining cavity resonance and minimizing noise couplings to achieve high sensitivity.

Contribution

It introduces the major design features of LIGO's length and frequency sensing and control system, crucial for maintaining resonance and reducing noise impacts.

Findings

Achieved differential length control within 5×10^-14 m of the operating point.

Outlined the control system's capability to reach the target strain sensitivity of 10^-21 rms.

Identified noise coupling restrictions and immunity requirements for optimal performance.

Abstract

Interferometric gravitational wave antennas are based on Michelson interferometers whose sensitivity to small differential length changes has been enhanced by adding multiple coupled optical resonators. The use of optical cavities is essential for reaching the required sensitivity, but sets challenges for the control system which must maintain the cavities near resonance. The goal for the strain sensitivity of the Laser Interferometer Gravitational-wave Observatory (LIGO) is 10^-21 rms, integrated over a 100 Hz bandwidth centered at 150 Hz. We present the major design features of the LIGO length and frequency sensing and control system which will hold the differential length to within 5 10^-14 m of the operating point. We also highlight the restrictions imposed by couplings of noise into the gravitational wave readout signal and the required immunity against them.