Internal reflection spectroscopy is a well established method for the study of surfaces and surface layers[1]. In recent years, several internal reflection techniques have evolved which make use of various kinds of resonant electromagnetic modes (surface, guided, Fabry-Perot) which can be excited in the system under study when particular resonance conditions are satisfied. Their main advantage over the conventional internal reflection spectroscopy is a strong enhancement in sensitivity due to the build up of large electric fields at resonance. On the basis of the physical mechanisms involved, all these techniques can be grouped in three main types of spectroscopy:
Surface wave excitation spectroscopy. The energy of the incident beam is dissipated through the resonant excitation of surface waves (plasmons, polaritons) in the system under study.
Guided wave spectroscopy. A surface layer on the system under study acts as a wave-guide into which energy from the incident beam is coupled and carried away.
Resonant FTR (Frustrated Total Reflection) spectroscopy. A surface layer on the systen under study acts as a FTR optical cavity [2] into which energy from the incident beam is trapped and dissipated.