Interpretation of attenuated-total-reflection dips observed in surface plasmon resonance

We present an interpretation that differs from an accepted explanation for resonance excitation of surface plasmons (SPs) on a metal using an attenuated total reflection (ATR) method. The metal ATR phenomenon is well expressed in terms of wave optics and accompanies an enhanced evanescent field. The ATR curves and the electric field and absorption distributions in the film layer for the noble metals are simulated numerically using electromagnetic wave analysis. The calculation results provide interpretation that the ATR dips are caused by an absorption loss of the metals produced by enhanced electric fields rather than the energy loss of a transfer excitation to the SPs: the damping loss converted into the SPs or the damping absorption of the once-converted propagation SPs. The sharp ATR dips do not necessarily demonstrate the high-resonance excitations of the SPs, and the metal ATR phenomenon is not restricted to the SPR. (c) 2007 Optical Society of America.