How else to sort monochromatic waves?


The electric field strength of light waves coming from the Sun is of course oriented randomly. There were found some transparent compounds which allow a light wave to pass through only having definite direction of the wave field strength. They call them polarizers the most notable being Polaroid films, Tourmaline and Herapathite. Now when the light already polarized passes through a polarizer, the output light intensity naturally depends on the angle between the direction of polarization of the light and that of the polarizer. This is known as the Malus’s law (1810). Another way to get polarized light waves is reflection of light incident at such an angle that the reflected rays be perpendicular to the refracted ones. Such an angle of incidence is known as the Brewster’s angle (1815). It depends on refractive index of the reflecting medium and is about 53 and 56 degrees for water or glass respectively. The reason of that phenomenon is that medium’s dipoles exited by the incident wave electric strength which lies in the plane of incidence can only emit waves of the same polarization producing the refracted beam. Whereas in the direction perpendicular to refraction they are unable to emit waves polarized that way, which would be reflection. Thus the reflected beam is only left with waves of the orthogonal polarization.

Transmittence and reflectance for polarized waves

Augustin-Jean Fresnel quantitatively described polarization and derived the angular dependence of relative reflection ‘R’ and transmission ‘T’ for light polarized in the plane of incidence ‘p’ and across it ‘s’ (1820).


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