Law of Malus, refraction of light rays, polarizers

1809 brought its changes in the scientific world of society. An engineer from France E. Malius discovered a new way of polarizing light. While conducting experiments, he accidentally noticed that if the crystal is rotated around a beam reflected from a glass, the intensity of light can periodically either increase or decrease. But completely the light does not go out, but only intensifies or weakens, but only at a certain position of the crystal. The statement was called "the law of Malus", it was recognized in the academic community.

From physics it is known that light can be transformed into a plane-polarized beam. This happens with the use of special devices that can only pass through definitely directed oscillations. An example of this is the oscillations located parallel to the plane , transmitting light and perpendicularly detaining oscillations. As a polarizer, anisotropic media are used with respect to the vibration of a vector, such as crystals. The most famous for its natural origin is tourmaline. It absorbs rays of light sufficiently strongly that their electric vector is perpendicular to the visual axis, which also follows from the conclusion of the law of Malus. But that light, in which this element is parallel, is almost not absorbed. This explains why natural light passing through the crystal plate is absorbed only half and polarized linearly with an electric vector located parallel to the visual axis of the tourmaline.

A more convenient crystal that has exactly the same properties is a polaroid. It consists of artificially prepared colloidal films, which are necessary in order to obtain polarized light. As in tourmaline, the principle of operation is based on a single crystal that absorbs perpendicularly directed oscillations of light. And in this phenomenon the law of Malus is not expressed. Let us consider other examples.

But when the polarization of light rays occurs with refraction or reflection on the boundary with isotropic dielectrics - this is the law of Malus. He somewhat corrected the physical phenomena associated with the electric oscillations of light.

But the law of Malus, the derivation of which was formulated above, does not state that such a method of polarization is basic and unique. There are others.

Any device that is used to produce polar rays of light is called a polarizer. But it is studied and explored with the help of an analyzer.

For example, there are two crystals that are arranged one behind the other in such a way that the axes form an angle. The first will miss the light, in which the electric vector is parallel to its axis. The component of the beam intensity will be delayed by the second crystal. And after two polaroid it will pass with the same length of electric vectors. In other words, the ratio of these intensities will be proportional to the amplitude square.

Hence it follows that the light transmitted through the analyzer is equal in strength to the power of the ray that follows the polarizer and multiplied by the cosine of the angle squared between them. This relationship is the phenomenon that describes the law of Malus.

This also includes double refraction of light rays, which is the main property when passing through crystals. This is explained by the features that are present in the environment of the anisotropic in the propagation of light. For example, by directing a narrow light beam onto the spar crystal, passing through it, two separated beams run parallel to each other. This will happen in any case, even if the light on the crystal falls in the normal position. One of them is called ordinary and is an extension of the primary beam, and the second is unusual, since it has a deviation property.