Departmental Seminar

Improved laser stabilization for LISA: Combining cavity and arm locking control systems

Mr Jobin Thomas Valliyakalayil

The Laser Interferometer Space Antenna, or LISA, is a space-based interferometer that will detect Gravitational Waves (GWs) from a million solar mass black hole mergers to inform cosmology.  LISA operates in the 0.1 mHz - 1 Hz band with a displacement sensitivity of 10 pm/  [1]. To measure the small displacements, suppression of laser frequency noise is a critical part of these GW detectors. In the current LISA baseline, Pound-Drever-Hall (PDH) locking and Time-Delay-Interferometry (TDI) are utilised to reach the sensitivity goal. 

In this project, I worked on a novel laser stabilization for the LISA mission by locking the primary laser to two references concurrently – the on-board optical cavity and the arms of the interferometer (which is the most stable reference in the LISA mission). The locking scheme can be implemented using digital controllers with minimal or no hardware changes to the LISA baseline structures. The preliminary results indicate that the technique can lower the residual laser frequency noise in the LISA science band by over 3 orders of magnitude: from 30 Hz/   to as low as 7 mHz/   at 10 mHz, potentially allowing the requirements on TDI to be relaxed [2]. 

My seminar will focus on the theoretical work for LISA, the requirements on the controllers and an experimental approach to verify the viability of the hybrid control scheme using the two sensors. We are utilising an optical cavity similar to the one for the LISA mission, and an optical fiber of length 18 km to create a Mach-Zehnder interferometer. The controllers for the two sensors are digitally implemented using Moku-Pro, an FPGA-based device. I will discuss on the current progress of the experiment, the challenges in the setup, and my future plans.

[1] K. Danzmann et al. LISA: A Proposal in Response to the ESA Call for L3 Mission Concepts (2017)

[2] J.T. Valliyakalayil et al. Phys. Rev. D 105 062005 (2022)


Zoom link :

Date & time

Thu 1 Dec 2022, 3.30–4.30pm



Physics Studio & Zoom


Members of RSPE welcome


2 61250206