Suspension platform interferometer for the AEI 10\,m prototype: concept, design and optical layout

TL;DR

This paper presents the design, simulation, and initial testing of a suspension platform interferometer (SPI) for the AEI 10-meter prototype, aimed at stabilizing optical table motions with high precision.

Contribution

It introduces a novel optical layout for the SPI, analyzes cross-coupling and noise sources, and demonstrates a proof of principle for sensing table motion.

Findings

Optical design allows fully decoupled sensing of table motions.

Simulation confirms stabilization goals are achievable.

Proof of principle test validates the sensing scheme.

Abstract

At present a 10\,m prototype interferometer facility is being set up at the AEI Hannover. One unique feature of the prototype will be the suspension platform interferometer (SPI). The purpose of the SPI is to monitor and stabilise the relative motion between three seismically isolated optical tables. The in-vacuum tables are suspended in an L-shaped configuration with an arm length of 11.65\,m. The design goal of the SPI is to stabilise longitudinal differential displacements to a level of 100\,pm/$\sqrt{\mathrm{Hz}}$ between 10\,mHz and 100\,Hz and relative angular noise of 10\,nrad/$\sqrt{\mathrm{Hz}}$ in the same frequency band. This paper covers the design aspects of the SPI, e.g. cross-coupling between the different degrees of freedom and fibre pointing noise are investigated. A simulation is presented which shows that with the chosen optical design of the SPI all degrees of table motion can be sensed in a fully decoupled way. Furthermore, a proof of principle test of the SPI sensing scheme is shown.