First Experimental Evaluation of Stray Light Noise Modeling of kilometers-long Beam Tube Arms of Gravitational Wave Detectors
We present the results of the first experimental evaluation of stray light noise models for LIGO beam tube baffles. We combine the results of a testing campaign at LIGO Livingston and SIS simulations to get a model of backscatter and diffraction noise of select mid-arm baffles. Agreement to within a factor of $3-10$ is found between models and measured gravitational waHe strain. Two distinct regions of well-propagating motion were identified, at approximately $35Hz$ and $90Hz$, and these are visible in the strain signal as broadband features. Peaks with $Q \approx 100-1000$ were also found in the strain signal between $70Hz$ and$100Hz$. These are theorized to come from diffraction noise only, and are modeled using Q-factors measured from the strain. These models are also in good agreement with the strain signal. Other findings on the effect of auxiliary arm systems on stray light noise are discussed.