Coupling characterization and noise studies of the Optical Metrology System on-board the LISA Pathfinder Mission

TL;DR

This paper investigates the Optical Metrology System of the LISA Pathfinder, analyzing noise, coupling effects, and mitigation techniques to enhance precision in space-based gravitational wave detection.

Contribution

It provides the first comprehensive analysis of the complete OMS model, including noise limits, coupling parameters, and mitigation strategies for the LISA Pathfinder mission.

Findings

Identified sensor noise limits and coupling parameters.

Measured and characterized cross-coupling effects.

Developed algorithms to mitigate system imperfections.

Abstract

In this article we describe the first investigations of the complete engineering model of the Optical Metrology System (OMS), a key subsystem of the LISA Pathfinder science mission to space. The latter itself is a technological precursor mission to LISA, a space-borne gravitational wave detector. At its core, the OMS consists of four heterodyne Mach Zehnder interferometers, a highly stable laser with external modulator and a phase-meter. It is designed to monitor and track the longitudinal motion and attitude of two floating test-masses in the optical reference frame with a (relative) precision in the picometer and nanorad range, respectively. We analyze sensor signal correlations and determine a physical sensor noise limit. The coupling parameters between motional degrees of freedom and interferometer signals are analytically derived and compared to measurements. We also measure adverse cross-coupling effects originating from system imperfections and limitations and describe algorithmic mitigation techniques to overcome some of them. Their impact on system performance is analyzed in the context of the Pathfinder mission.