Effect of surface polaritons on the lateral displacement of a light beam at a dielectric interface

We consider the effect of surface polaritons on the shift of a beam of light of finite cross section on reflection from a two-layered semi-infinite medium. The beam is incident upon the first layer at an angle greater than the critical angle; the evanescent wave (in the first layer) interacts with the surface polariton at the interface between the first layer and the second layer. The plane-wave components of the incident "finite-cross-section" beam are absorbed and phase shifted by various amounts. The resultant emerging (reflected) beam, therefore, undergoes a shift. It is found that the calculated shift can assume very large values.