Spot size estimation of flat-top beams in space-based gravitational wave detectors

Motivated by the necessity of a high-quality stray light control in detection gravitational waves space, spot size flat top beam generated clipping Gaussian (GB) is studied. By adopting mode expansion method (MEM) approach to simulating beam, slight variant definition mean square deviation (MSD) for MEM proposed. This enables us quickly estimate arbitrary propagation distances. Given that degree dependent on power ratio within surface an optical element, MSD range used as measure size. The then validated cases simple astigmatic and nearly-Gaussian profiles. As representative example, top-hat science interferometer space simulated. traditional analysis, divergent when diffraction taken into account. A careful error analysis carried out divergence present context, it argued this will have little effect our estimation. Using results study allows optimal design systems with or other types non-Gaussian beams. Furthermore, testing interferometry space-based wave detectors simulations. work serve useful guide future system bench sizes components.