Fluctuating electromagnetic fields of solids

Various theoretical methods to calculate the spectral and correlation properties of fluctuating electromagnetic fields generated by solids are reviewed, all of which essentially reduce to solving the Maxwell equations for a specified geometry and boundary conditions and then using the fluctuation–dissipation theorem. The spectral and correlation properties of thermally stimulated fields of a system in equilibrium and out of equilibrium with surrounding bodies are described. A special attention is put to the difference between the spectral and correlation properties of the propagating and evanescent waves of the thermally stimulated fields of solids. The dispersion interaction between solid bodies in different thermodynamic states, the resonance dispersion interaction in a three-body system, the fluctuating fields as a means of body-to-body energy transfer, and the shift, broadening, and deexcitation of energy levels in a particle near a solid surface are discussed using the theory of thermally stimulated electromagnetic fields. Thermally stimulated emission of infrared radiation of semiconductor crystals and films (heated up to 150 °C) on metal substrates are measured in frequency range of vibrational polaritons both for propagating waves and for evanescent waves transformed into propagating waves due to ATR prism over the samples. The experimental results on thermally stimulated electromagnetic fields from solids are in qualitative and quantitative agreement with model calculations and theoretical expectations.