Arm-Locking with the GRACE Follow-On Laser Ranging Interferometer

TL;DR

This paper proposes using the GRACE-FO Laser Ranging Interferometer to demonstrate arm-locking, a technique for stabilizing laser frequency in space-based interferometers, showing promising noise suppression and manageable frequency pulling.

Contribution

It designs an arm-locking controller for GRACE-FO and demonstrates through simulations that effective laser frequency stabilization is feasible in orbit.

Findings

Achieves ~100x reduction in laser frequency noise at 1Hz

Pulling of the master laser frequency is less than 100 MHz

Feasibility of on-orbit arm-locking demonstration is supported

Abstract

Arm-locking is a technique for stabilizing the frequency of a laser in an inter-spacecraft interferometer by using the spacecraft separation as the frequency reference. A candidate technique for future space-based gravitational wave detectors such as the Laser Interferometer Space Antenna (LISA), arm-locking has been extensive studied in this context through analytic models, time-domain simulations, and hardware-in-the-loop laboratory demonstrations. In this paper we show the Laser Ranging Interferometer instrument flying aboard the upcoming Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission provides an appropriate platform for an on-orbit demonstration of the arm-locking technique. We describe an arm-locking controller design for the GRACE-FO system and a series of time-domain simulations that demonstrate its feasibility. We conclude that it is possible to achieve laser frequency noise suppression of roughly two orders of magnitude around a Fourier frequency of 1Hz with conservative margins on the system's stability. We further demonstrate that `pulling' of the master laser frequency due to fluctuating Doppler shifts and lock acquisition transients is less than $100\,$MHz over several GRACE-FO orbits. These findings motivate further study of the implementation of such a demonstration.