Аннотация:We propose a universal method of computation of thermal noise in mirrors of gravitational wave
interferometers based on first principles. We imagine a situation where a mirror is part of a Fabry–Perot
cavity. The movement of the mirror’s surface produces variation of the eigen frequency of the cavity,
which is computed by evaluating the variation of the energy stored in cavity. We consider two particular
examples: first, the thermal noise from a dielectric slab inside the Fabry–Perot cavity, and second, the
polarization-dependent thermal noise in the folded cavity.