Stray Light Challenges in LISA Interferometry: Sources, Dynamics, and Mitigation Strategies

• Katharina-Sophie Isleif (HSU (Helmut-Schmidt-Universität), DESY)

Room: SR 4 In space-based gravitational wave observatories like LISA, achieving sub-picometer (urad) precision at frequencies below 1Hz is essential for detecting cosmic events such as black hole mergers, neutron star collisions, and galactic interactions. However, interferometric sensitivity is compromised by stray light—unwanted laser beams that propagate within the main interferometer and interact with other beams, forming competing interferometers. This interaction results in phase errors that can limit the urad precision. In this presentation, we categorize types of stray light, including ghost beams and fiber Rayleigh backscatter, and predict their impact on phase errors using the small-vector noise model. We emphasize the critical influence of stray light's amplitude and phase on phase errors and highlight the need for environmental stability, such as temperature and air density control, to mitigate these errors. We will present comparisons between simulation data and experimental data from the LISA backlink fiber, affected by fiber length noise due to fiber Rayleigh backscattering. Our findings demonstrate that environmental stabilization can significantly reduce phase errors. Additionally, we explore various mitigation strategies, including beam baffles, balanced detection, frequency shifting, digital interferometry, and optimizing interferometer designs through IfoCAD optical simulations. These strategies are designed to obstruct stray light beams from inducing phase errors on the photodiode, thus enhancing measurement precision crucial for LISA and advancing the sensitivity of gravitational wave detection and other high-precision experiments.