Evanescent Waves and the Goos-Hänchen Effect
The reflection of electromagnetic waves from a dielectric interface is usually studied by assuming the incidence of plane waves having infinite spatial extent; in addition, the radiation is also assumed to be purely monochromatic (see, e.g., Reitz and Milford, 1962). Both these concepts are introduced for simplicity in theoretical considerations. In practice, one encounters a finite-width beam that extends over a finite time and hence does not remain monochromatic. In this chapter we shall study the total internal reflection of a bounded beam by a plane dielectric interface and we shall show that the beam appears to undergo a lateral shift as shown in Fig. 11.1a. This displacement of the beam was experimentally studied by Goos and Hänchen. Hence this effect is called the Goos-Hänchen effect.* This shift cannot be explained from ray-optic considerations and is a consequence of the evanescent field set up in the rarer medium. Since evanescent fields are of great importance in electromagnetic theory,† we thought it worthwhile devoting a chapter to a phenomenon that brings out many salient features associated with the evanescent field.
KeywordsCritical Angle Total Internal Reflection Evanescent Wave Planar Waveguide Poynting Vector
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