Fresnel’s equations describe how light transmits through a dielectric interface by calculating how much of the incident light passes into the second medium when it encounters a boundary between two transparent materials with different refractive indices.
When light strikes the boundary, some of it is reflected back into the original medium, and the rest is transmitted into the second medium at a different angle. Fresnel’s equations determine the proportion of transmitted light based on the angle of incidence, the refractive indices of both media, and the polarization of the light.
For light with electric fields perpendicular to the plane of incidence (s-polarized), and light with electric fields parallel to the plane of incidence (p-polarized), the transmission behavior is different. The equations show that transmission generally decreases as the angle of incidence increases, especially for light approaching at shallow angles.
Fresnel’s equations also take into account the fact that light changes direction when entering a new medium, a behavior described by Snell’s law. The transmitted light depends on how steeply the wave strikes the interface and how much the refractive index changes across the boundary.
In essence, Fresnel’s equations explain how much light is transmitted into the second material and how this varies with angle and polarization, which is crucial in designing lenses, coatings, and other optical components.