Electric Field Components in Bulk Rare Optically Thin Medium

Electric Field Components in Bulk Rare (Optically Thin) Medium 

The incident plane wave has only field components perpendicular to the direction of propagation. In contrast, the evanescent field has components along all directions X, y, and z of a Cartesian coordinate system attached to the IRE, as shown in Fig. 2. The direction of the incident field vector can be selected by use of a polarizer. The symbols II and denote electric field vectors parallel and perpendicular to the 

The above equations are exact only for non-absorbing rare media, but are very good approximations for weakly absorbing samples. Note that 7i 2 7 j2 0-2 

Equations (4)-(6) hold for a bulk (non- or weakly absorbing) rare medium 2 (case (a) in Fig. 3). In the case of a thin film with thickness 7 7p in contact with the IRE (case (b) in Fig. 3), the thin-layer approximation gives good results (5). Here it is assumed that the electric field is determined by the IRE and the bulk medium above the thin film. The thin film is then considered as a dielectric in this field, and equations similar to Eqs. (4)-(6) can be derived. 

Equations (7) and (8) have to be used to calculate the effective thickness (for a bulk medium 2), according to the following  

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