A strong maximum of absorption (as much as 100%) of bulk TM electromagnetic waves by an ultrathin film with imaginary dielectric permittivity is shown to exist at some optimal film thickness. This typical thickness is usually much smaller than the wavelength and the wave penetration depth in the material of the film. The absorptivity maximum increases and the typical thickness decreases with increasing dielectric permittivity of the layer. An optical analog of linear (liquid) friction is discussed. A frictional contact approximation for TM electromagnetic waves is analyzed, and relevant boundary conditions with an optical coefficient of friction are derived.
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