On the non-existence of the so-called “electric field standing wave effect” in transflection FTIR spectra

The so-called Electric Field Standing Wave (EFSW) Effect has been used by several groups to explain the experimental observation that relative absorbance in FTIR spectra varies with thickness of biomedical samples mounted on a reflective slide. Here, by involving both electric and magnetic fields of an electromagnetic wave, we establish, by classical optical analysis, that there is no such effect. Furthermore, application of multi-interface Fresnel-like simulations to three different systems shows that reflections, transmission and consequent interferences at the “vacuum”/sample interface are solely responsible for the dependence of relative band heights on sample thickness.