Thermodynamical fluctuations in optical mirror coatings

Thermodynamical (TD) fluctuations of temperature in mirrors may produce surface fluctuations not only through thermal expansion in mirror body [Phys. Lett. A 264 (1999) 1] but also through thermal expansion in mirror coating. We analyze the last 'surface' effect which can be larger than the first 'volume' one due to larger thermal expansion coefficient of coating material and smaller effective volume. In particular, these fluctuations may be important in laser interferometric gravitational antennae