Malus law

There are devices called polarizers, sensitive to polarization of a light beam. These devices freely transmit the incident electromagnetic waves with a plane of oscillation parallel to the plane of the polarizer, and completely absorb oscillations perpendicular to this plane. Hence, behind the polarizer the natural light becomes polarized with the plane of oscillation parallel to the plane of the polarizer. If, in the way of this secondary beam, a second polarizer is installed with a plane perpendicular to the first, it will detain the first polarized beam completely. This second polarizer is in the position of an analyzer it is sensitive to the degree of polarization of the light beam. 

This equation is called Malus law. It can be seen that if the wave s plane of oscillation is parallel to the polarizer axis, the beam will pass through with no intensity loss (cp = 0, cos (p = 1). In contrast, at cp = nil cos tp = 0 and light will be absorbed completely. 

If natural light falls on a polarizer the intensity of the passed light is proportional to average value of (cos tp) since in an interval 0 (p ti/2 the value (cos tp) is equal to 1/2, /poi. = intensity of light passed through the polarizer is a half of that of the incident natural light. 

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For intermediate angles, the fraction of intensity transmitted is given by the square of the co-sine of the angle (Malus law). This is easily understood as the electric field vector can be decomposed in two orthogonal components, one along the polarization axis that is transmitted, and one along the perpendicular direction that is absorbed. Since intensity is proportional to the square of the electric field amplitude, the Malus law follows. 

Figure 6.22 Illustration of Malus law (1) the polarization device and (2) the plane of polarization.

When a polarizer is rotated with respect to the polarization plane of already polarized incident radiation the transmitted intensity obeys the law of Malus... 

The intensity of plane-polarized light beam passing through a polarizer is given by the law of Malus as... 

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