Spectral composition of electromagnetic fluctuations induced by a lossy layered system



We calculate the spectral characteristics of fluctuating electromagnetic fields generated by a half-space covered with a film of an arbitrary thickness. Materials of the half-space and the film are described by different complex permittivities. Expressions for spectral power densities of fluctuating fields and all spatial derivatives expressed via Fresnel coefficients for “p” and “s” waves are derived. Various limiting cases for propagating and evanescent waves in cases of different film thickness are considered. Possible contributions to spectral power densities from interface excitations and wave-guide modes are discussed by analyzing the Fresnel factors in the expressions. Using the results for spatial derivatives a closed analytical expression for a multipolar force acting on a small particle near a half-space is found for multipoles of all orders. The case for a dipole interaction follows directly from a general solution.