Speaker
Description
Accurately projecting scattered light noise requires two steps: simulating the steady-state field within long arm cavities and translating these results into strain noise. I will present recent advancements in both directions toward a more robust stray-light modeling framework for 3G observatories. Standard paraxial, free-space FFT propagation tools neglect beam tube boundary effects. By introducing a waveguide-like modal description, I will show that while the tube boundary reshapes the large-radius field structure, dense internal baffling effectively acts as a spatial filter that suppresses couplings from potential tube defects. In densely baffled regimes, tube boundary effects become subdominant, validating the continued use of standard FFT codes for baffle layout optimization. To convert these simulation results into strain noise, current noise budgets rely on analytical models from the initial LIGO/Virgo era, which fail to capture the complex frequency-dependent filtering of modern detector topologies. Using the two-photon formalism, we derive more accurate scattered-light strain noise projections, demonstrating that accounting for the full optomechanical response is essential for precise estimations in 3G designs.