Thermally induced refractive index fluctuations in transmissive optical components and their influence on the sensitivity of Einstein telescope

Abstract

With a relative length measurement precision of better than 10−23, gravitational wave interferometers are the most precise instruments that have ever been built. With this enormous sensitivity many noise sources potentially effect gravitational wave detector sensitivity, each of which must be investigated to ensure confidence in design sensitivity. We present calculations of photoelastic noise as well as thermo refractive noise in the beam splitter and the input test masses in Einstein telescope (ET). It turns out that the amplitude of the photoelastic noise in the ET low-frequency detector is about five orders of magnitude below the maximum design sensitivity and five orders of magnitude below that of the ET high-frequency detector, whereas thermo refractive noise impairs the design sensitivity by approximately 20%.