Spectral composition and spatial distribution of thermal fields near a solid surface

The relative contributions of the evanescent and propagating waves at different distances from the total thermally stimulated electromagnetic fields generated by solids are studied. We analyzed both the spectral power densities of different polarizations and integrated quantities over the whole spectral range. A detailed analysis of the spatial structure of thermal electromagnetic fields near a sample surface is performed and illustrated. It is graphically shown that thermal fields near a surface are mainly represented at the frequencies of the eigenmodes (normal modes) of the system under study. We illustrate the limits of applicability of known simple analytic approximations of the general formulas for thermal fields in the near and far zones. The influence of the details of the density of states of thermal fields on the integral quantity of the energy is explained. Furthermore, the complex spectra of thermal fields of different polarizations generated by the plane-layered structure are graphically analyzed. Such spectra consist of different resonances corresponding to the whole set of the surface polaritons, the Fabry–Perot and waveguided modes of the system under study. We also estimate the total energy of the evanescent thermal fields around the heated sample and show that this energy is much smaller than the thermal energy stored inside the heated solids. (paper)