Speaker
Description
Surface roughness on optical components produces scattered light that can limit the performance of gravitational-wave detectors, such as the Einstein Telescope (ET).
We present studies on how accurately standard paraxial numerical tools reproduce this scattering in ET-relevant regimes. We compare FFT-based propagation and Hermite-Gaussian modal simulations, with paraxial and non-paraxial propagation methods. This allows us to identify where the tools become limited by grid resolution and mode truncation, respectively.
Mirror surface quality is often discussed using power spectral density (PSD), which describes its spatial-frequency content. PSD-based descriptions have so far been sufficient to support modelling, but ET places more stringent requirements. This motivates the need to understand in more detail how these descriptions relate to the distribution of scattered light, and which parts of the scattered light distribution are correctly reproduced by the standard simulation tools. We present validation results and provide recommendations for the use of PSD-based mirror surface descriptions.