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 15 pm/√Hz [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.

My talk focuses on a novel laser stabilization for the LISA mission by locking the primary laser to two references simultaneously – 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 optical baseline hardware. 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, improving the margin for TDI [2].

I will also discuss a bench-top experiment that would be analogous to the LISA mission. In the experiment, we lock a 1064nm laser to a fixed-length ultra-stable cavity, like the one proposed for LISA, and a fiber-based Mach-Zehnder using a 10 km fiber. The controllers for the two sensors are digitally implemented using Moku-Pro, an FPGA-based device. The results from this demonstration is presented and compared to analytical models of the control system. This experiment validates the viability of the hybrid arm-cavity stabilization for the LISA mission.

[1] M. Colpi et al., LISA Definition Study Report (2024)

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