Speaker
Description
New experiments are being developed without the background of quantum shot noise to look for weak, high frequency signals using Michelson interferometers. Since shot noise is no longer the dominant noise source with these readout schemes, it is important to accurately model thermal noise to characterize the signal and design more sensitive experiments. However, previous modeling uses approximations that are no longer valid in these frequency regimes. In the MHz band with millimeter-scale mirrors and in the kHz band with meter-scale mirrors, the quasi-static approximation no longer applies. We therefore develop more general models of substrate and coating Brownian noise, substrate and coating thermoelastic noise, and coating thermorefractive noise. We validate the models with comparisons to previous low frequency modeling and high frequency spectra from experiments that have already taken data, the Holometer and QUEST. We then apply the new models to upcoming experiments, GQuEST and Cosmic Explorer.