Propagation of IR Radiation through Planar Interface between Two Isotropic Media

PROPAGATION OF IR RADIATION THROUGH PLANAR INTERFACE BETWEEN TWO ISOTROPIC MEDIA 

Let an electromagnetic wave propagating in medium 1 with refractive index hi encounter at z = 0 (Fig. 1.8) an ideal planar surface of medium 2 characterized by W2 ni. At the interface, the incident wave splits into the reflected and transmitted (across the interface) components (Fig. 1.8). What are the directions and intensities of these components Consider first the case when both contacting media are transparent (ki =k2 = 0). 

Law of reflection. The incident ray, the reflected ray, and the normal to the interface at the point of incidence all lie in the same plane (the plane of incidence). The angle of incidence cpi is equal to the angle of reflection (p fVig. 1.8)  

All the angles are measured with respect to the surface normal (Fig. 1.8). 

The reflection from the boundary when medium 1 is optically rarer than medium 2 (pi U2) is called the external or specular s reflection (Fig. 1.8). When the radiation travels from an optically denser to optically rarer medium, that is, when n n2, it is said that internal reflection takes place (see Fig. 1.10 below). 

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