Spectroscopy by Evanescent Surface Waves

As a rule these methods are based on the concept of evanescent surface waves caused by total internal reflection at a solid/liquid interface. In order to understand the so-called evanescent spectroscopy, a simplified theory of total internal reflection is given below. More complete treatments can be found in various specialized monographs and reviews 145 147 . 

The magnitude of E1,0 can be calculated from Fresnel s law. If the electric field amplitude as a function of distance z is expressed per unit of incident electric field amplitude, E 0, of the perpendiculary polarized electromagnetic wave, then  

From an experimental point of view it is important to recognize that the profile of (Ey2 as a function of z is proportional to the profile of the intensity of electromagnetic radiation in the proximity of the interface in medium 2. Such a profile will determine the surface sensitivity of the evanescent wave the depth of penetration is smaller if  

choosing the experimental parameters one can design a sensing profile to a particular need. It has to be mentioned that in this simplified derivation of evanescent spectroscopy theory two implicit assumptions were made  

Both media are nonabsorbing, only real refractive indices were being used,1 and 

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