From Big Medical Encyclopedia

POLARIZATION OF LIGHT — orderliness in orientation of a vector of tension electric (and unambiguously related magnetic) fields of a light wave in the plane, perpendicular to the direction of distribution of a light ray. On P. the page based operation of the devices used in medicine for definition of concentration of optically active substances (e.g., sugars), for studying biochemical, reactions, a structure of molecules (see. Microscopic methods of a research , Microspectral analysis ). P.'s phenomenon of page is the cornerstone of the optical devices serving for protection of eyes of the driver from dazzle as bright light of headlights of counter transport at night. It finds various application in the equipment, in particular at routine control, etc.

Fig. 1. The graphic representation of the unpolarized (natural) light (a) which is partially polarized and completely linearly polarized: shooters showed the direction of fluctuations of electric vectors of a light wave in the plane, perpendicular to the direction of distribution of a light ray. It is visible that in a natural, unpolarized, light ray (a) the electric vector of a light wave can be sent to any party; at partial polarization (b) restriction in the direction of the plane of fluctuations of an electric vector of a light wave appears: in case of full linear polarization (v) the direction of an electric vector of a light wave is limited to one plane (in this case down).

The light wave, as well as all electromagnetic oscillations, is characterized by certain values of vectors of tensions variable electric (E) and magnetic (N) of fields (on absolute values and the directions). Graphically it is often represented in the form of projections of a vector of E in each point of a light wave on the plane, perpendicular to the direction of its distribution (fig. 1).

Though the light wave which is let out by any elementary radiator (atom, a molecule) is always completely polarized (see. Luminescence , Molecule ), for the total light wave radiated by a body in general (it is formed as a result of addition of radiation of a set of radiators), the orientation of an electric vector which is randomly changing in time is characteristic (all directions of fluctuations of a ravnoveroyatna, and amplitudes are identical). Such light wave is called natural, or unpolarized.

Fig. 2. The graphic representation of distribution linearly - the polarized light wave (Z) and its components — vectors of voltage (E) and magnetic (N) of fields.

If fluctuations of E happen in various directions, but in nek-ry of them amplitude of a vector of E is more, than in others, then such wave is called partially polarized. Graphically generally the end of a vector of E completely polarized waves describes on the plane, perpendicular to the direction of distribution of a wave, an ellipse — so-called elliptic polarization. Are most widespread circular and linear P. of page (fig. 2). In the latter case fluctuations of a vector of E happen constantly only in one direction. The plane passing along the direction of distribution of a wave and the direction of a vector of electric field is called the plane of fluctuations, and the plane, perpendicular to it and matching the direction of a vector of N — the plane of polarization.

P.'s phenomenon of page can arise in the course of emission of light (see. Lasers ), its dispersion, reflection and refraction (see. Optics ), during the passing of light through optically active substances — some crystals, solutions of sugars, organic to - t, alkaloids etc. Optically active substances find property not only to linearly polarize light, but also to rotate the plane of polarization (see. Polarimetry ).

Fig. 3. Nicol. The directions of fluctuations of a vector of E in the plane of the drawing are shown by shooters, perpendicular to the plane of the drawing — an arrow with points; blackening on the lower side of a prism provides full absorption of the beam reflected from the plane of gluing together.

For linear polarization of light in polarizing devices use, as a rule, polarizing prisms and films (polaroids), and for obtaining radiation with circular polarization — more difficult devices. Property of optically active crystals to differently refract components of a ray of light (see is the cornerstone of work of a polarizing prism. Double refraction ), polarized in mutually perpendicular planes (so-called ordinary and unusual beams). One of these beams (unusual is more often) and is used as a source of the polarized light, and the second is taken aside or extinguished. The elementary polarizing prism consisting of two trihedral prisms is the eurysynusic polarizing nicol (fig. 3).

P.'s phenomenon of page is widely used in scientific research, the equipment etc. At polarizing researches measure extent of change of P. of the page caused by interaction of light with the studied object or optical activity (i.e. dependence of size of rotation of the plane of polarization linearly - the polarized light from concentration of substance during the passing through optically active substance). Registration of rotary dispersion (i.e. changes of an angle of rotation at change of wavelength of light) allows to define concentration of a number of substances and to study their structure. For P.'s measurement by the village polarimeters and spektropolyarimetra use devices (see. Polarimetry ).

Bibliography: Zhevandrov N. D. Anisotropy and optics, M., 1974; Lande-@ e r of G. S. Optik, M., 1976.

V. N. Verkhoturov.