The complex dielectric constant of Fe has a large imaginary part and small real part throughout most of the visible region (∊i ≫ |∊r|). Under this condition a thin film of Fe(≤ 20 nm), bounded by a dielectric, can support a surface polariton. For p-polarized fields the antisymmetric solution to the dispersion relation has a nearly real propagation vector parallel to the surface. Hence this antisymmetric polariton can be excited optically. We use the attenuated total reflection (ATR) configuration with three successive layers, cryolite-Fe-cryolite, evaporated onto the base of a glass prism. The surface polariton is detected as a narrow minimum in the ATR angular spectrum. We choose the frequency at which ∊r = 0 and then an incident p-polarized plane wave yields zero energy propagation in the Fe film in the direction parallel to the plane on the film. There are also other broader minima in the p-polarized spectrum corresponding to large field oscillations localized in the second dielectric. Minima in the s-polarized spectrum correspond to oscillations localized in the first dielectric. In addition the angular reflectance spectrum of both polarizations contains sharp maxima caused by resonance standing wave patterns which persist through the incident medium as well as the film system.
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