Open resonator model for Attenuated Total Reflection dips

Attenuated Total Reflection (ATR) dips are interpreted in terms of an open resonator model, in which the evanescent field serves as a lossless energy storage element and the coupling and damping is determined by the properties of a thin metal layer. The appearance of the dips is related to the Brewster condition, without referring to the dispersion relation of Sommerfeld–Zenneck like surface modes. A strong ATR response is conditioned by the relation θ c r i t ≤ θ B r e w s t e r ≤ 9 0 ∘ with the critical angle θ c r i t . Outside of this range only a weak response, i. e., a low field enhancement, is found, even though the reflectivity can become very small. The conditions are in this case comparable to the case of the resonant absorber, a related phenomenon, which can be observed in thin dielectric layers.