**INTERFERENCE OF WAVES** — the addition in space of two or several waves which is followed depending on a phase ratio of the composed waves by the alternating strengthening or weakening of the resulting wave. Phenomenon And. it is peculiar to wave fluctuations of any nature century (e.g., electromagnetic, sound, to fluctuations on the surface of liquid etc.) and it is possible only in that case when summable fluctuations of a kogerentna (are coordinated among themselves), i.e. have the identical wavelength and invariable shift of phases in each summable point.

At addition of two coherent harmonious (sinusoidal) waves with identical amplitudes (E1 = E2 = E) and the identical direction of fluctuations amplitude of a total wave (EU) in a specific point of space is equal in the elementary case:

Ec = √ (E1^2 + E2^2 + 2E1E2cosφ) = E √ (2(1 + cosφ)),

where φ — a difference of phases of summable fluctuations in this point. From the given expression it is visible that if cosφ = +1, φ = 2πn where n = 0,1, 2..., total amplitude is equal 2E; if cosφ =-1

[φ = π(2n+1), where p = 0, 1,2...],

total amplitude is equal to 0. Thus, for receiving an interference pattern it is necessary to put two coherent fluctuations which difference of phases changes from a point to a point, remaining a constant for each of these points. These conditions are satisfied, e.g., at addition of monochromatic light waves (see. Light ), reflected from a front and back surface of a clear film of variable thickness. The waves which are summed up on a front surface will have the difference of phases determined by length of the way passed by the wave reflected from a back surface of a film (i.e. determined by film thickness). In places of a film for which the difference of phases has values equal and close 2πn (where p — any integer) ghost lines and where the difference of phases is equal and close π (2n +1) — dark strips will be observed. At the same time each specific strip corresponds to a certain film thickness.

On use of the phenomenon And. century operation of interferometers is based (see. Refractometry ) and interferential microscopes (see) which apply to determination of optical parameters of solutions during the carrying out a wedge, analyses and studying of structure medical - biol, objects (see. Microscopic methods of a research ). For medical diagnosis the increasing application is found by holographic interference microscopes and endoscopes which main advantage are dimensions of the image, high resolving power and accuracy of measurement (see. Holography ). By means of these devices studying of soft tissues and internals, carrying out localization of foreign bodys, studying of a microstructure and dynamics of processes, determination of geometrical parameters any biol, objects and their changes is possible (e.g., erythrocytes of the person). Attempts to create Ophthalmolum, the equipment for objective diagnosis of vision disorders on the basis of interferometric techniques which accuracy more than by 100 times exceeds the accuracy of stereophotogrammetric methods are made.

**Bibliography:** Kolyer R., Berkhart To. and Lin L. Optical holography, the lane with English, M., 1973; The Elementary textbook of physics, under the editorship of G. S. Landsberg, t. 3, M., 1972.

*V. Verkhoturov.*