Coating thermal noise of a finite-size cylindrical mirror

Thermal noise of a mirror is one of the limiting noise sources in the high-precision measurement such as gravitational-wave detection, and the modeling of thermal noise has been developed and refined over a decade. In this paper, we present a derivation of coating thermal noise of a finite-size cylindrical mirror based on the fluctuation-dissipation theorem. The result agrees to a previous result with an infinite-size mirror in the limit of large thickness, and also agrees to an independent result based on the modal-expansion method with a thin-mirror approximation. Our study will play an important role not only to accurately estimate the thermal-noise level of gravitational-wave detectors but also to help in analyzing thermal noise in quantum-measurement experiments with lighter mirrors.