Sensitivity improvement of a laser interferometer limited by inelastic back-scattering, employing dual readout

TL;DR

This paper introduces a dual readout method using dual homodyne detection to subtract inelastic back-scattering signals, significantly enhancing the sensitivity of laser interferometers used in gravitational-wave detection.

Contribution

It presents a novel dual readout scheme that models and subtracts parasitic back-scattering signals, improving measurement sensitivity beyond traditional veto methods.

Findings

Back-scattering noise reduced in a table-top Michelson interferometer.

Subtraction method improves the spectral density of measurement noise.

Potential to enhance sensitivity of future gravitational-wave detectors.

Abstract

Inelastic back-scattering of stray light is a long-standing and fundamental problem in high-sensitivity interferometric measurements and a potential limitation for advanced gravitational-wave detectors. The emerging parasitic interferences cannot be distinguished from a scientific signal via conventional single readout. In this work, we propose the subtraction of inelastic back-scatter signals by employing dual homodyne detection on the output light, and demonstrate it for a table-top Michelson interferometer. The additional readout contains solely parasitic signals and is used to model the scatter source. Subtraction of the scatter signal reduces the noise spectral density and thus improves the measurement sensitivity. Our scheme is qualitatively different from the previously demonstrated vetoing of scatter signals and opens a new path for improving the sensitivity of future gravitational-wave detectors and other back-scatter limited devices.