Enhancement of Sensitivity-Bandwidth Product of Interferometric GW Detectors using White Light Cavities

TL;DR

This paper proposes a new design for white light cavities in gravitational wave detectors, significantly enhancing their sensitivity and bandwidth, enabling better detection of gravitational waves.

Contribution

It introduces a general model for GW detectors with white light cavities and a practical, non-invasive design for improved sensitivity and bandwidth in AdLIGO.

Findings

Enhanced sensitivity and bandwidth over planned AdLIGO levels.

A simple, robust design of a compound mirror for WLC integration.

Potential to cover the entire spectrum of interest for gravitational waves.

Abstract

The effect of gravitational waves (GWs) has been observed indirectly, by monitoring the change in the orbital frequency of neutron stars in a binary system as they lose energy via gravitational radiation. However, GWs have not yet been observed directly. The initial LIGO apparatus has not yet observed GWs. The Advanced LIGO (AdLIGO) will use a combination of improved techniques in order to increase the sensitivity. Along with power recycling and a higher power laser source, the AdLIGO will employ signal recycling (SR). While SR would increase sensitivity, it would also reduce the bandwidth significantly. Previously, we and others have investigated, theoretically and experimentally, the feasibility of using a White Light Cavity (WLC) to circumvent this constraint. However, in the previous work, it was not clear how one would incorporate the white light cavity effect. Here, we first develop a general model for Michelson-Interferometer based GW detectors that can be easily adapted to include the effects of incorporating a WLC into the design. We then describe a concrete design of a WLC constructed as a compound mirror, to replace the signal recycling mirror. This design is simple, robust, completely non-invasive, and can be added to the AdLIGO system without changing any other optical elements. We show a choice of parameters for which the signal sensitivity as well as the bandwidth are enhanced significantly over what is planned for the AdLIGO, covering the entire spectrum of interest for gravitational waves.