Experimental demonstration of the combined arm- and cavity-locking system for LISA

TL;DR

This paper experimentally demonstrates a hybrid laser locking system combining arm and cavity references for LISA, showing significant noise suppression and potential improvements in gravitational wave detection sensitivity.

Contribution

It provides the first experimental verification of a hybrid arm-cavity locking scheme designed to improve LISA's laser stability with minimal hardware changes.

Findings

21 dB suppression of cavity fluctuations

Reduced Doppler pulling of laser frequency

Viability of hybrid locking for LISA

Abstract

Laser frequency noise suppression is a critical requirement for the Laser Interferometer Space Antenna (LISA) mission to detect gravitational waves. The baseline laser stabilization is achieved using cavity pre-stabilization and a post-processing technique called Time-Delay-Interferometry (TDI). To enhance the margins for TDI, alternate laser locking schemes should be investigated. A novel stabilisation blending the excellent stability of the arm with the existing cavity reference has been shown theoretically to meet the first-generation TDI margins. This locking system was designed to be implemented as a firmware change and have minimal or no changes to the LISA hardware. This paper experimentally verifies the hybrid laser locking technique by utilizing two references - an optical cavity, and an interferometer with delay imparted using 10 km of optical fiber. The results indicate the viability of the combination of arm-cavity locking system for LISA. They show the key benefits envisioned by this technique; suppression of the cavity fluctuations by the arm sensor (by 21 dB in this demonstration) and reduction of Doppler pulling of the laser frequency, a key technical challenge for arm locking.