5 M ay 2 00 3 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 [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.