Picometer Sensitive Prototype of the Optical Truss Interferometer for LISA

TL;DR

This paper presents a prototype optical truss interferometer capable of picometer-level sensitivity, designed for verifying the optical path stability of LISA telescopes, with potential applications in ground testing and other systems.

Contribution

The paper introduces a novel, highly sensitive optical truss interferometer prototype demonstrating 1 pm/√Hz stability for telescope verification.

Findings

Achieved 1 pm/√Hz sensitivity in prototype measurements

Demonstrated stable measurement of optical cavities with fiber-coupled units

Analyzed noise sources limiting the measurement sensitivity

Abstract

The optical truss interferometer (OTI) is a contingent subsystem proposed for the LISA telescopes to aid in the verification of a $1 \frac{\mathrm{pm}}{\sqrt{\mathrm{Hz}}}$ optical path length stability. Each telescope would be equipped with three pairs of compact fiber-coupled units, each forming an optical cavity with a baseline proportional to the telescope length at different points around the aperture. Employing a Pound-Drever-Hall approach to maintain a modulated laser field on resonance with each cavity, the dimensional stability of the telescope can be measured and verified. We have designed and developed prototype OTI units to demonstrate the capability of measuring stable structures, such as the LISA telescope, with a $1 \frac{\mathrm{pm}}{\sqrt{\mathrm{Hz}}}$ sensitivity using a set of freely mountable fiber-injected cavities. Aside from its initial motivation for the telescope, the OTI can also be readily integrated with other systems to aid in ground testing experiments. In this paper, we outline our experimental setup, measurement results, and analyses of the noise limitations.