![]() ![]() In order to find out the nature of the interference of secondary waves emitted in other directions, we divide the slot surface into n identical zones (they are called Fresnel zones) and consider the direction for which the condition is satisfied: Therefore, in the center of the screen (O) there is maximum interference for waves of any length. All secondary waves emitted from the surface of the slot in the direction parallel optical axis of the lens (α = 0), come into focus of the lens in the same phase. Behind the slit (parallel to its plane) we place a converging lens, in focal plane which we place the screen E. Let a plane monochromatic light wave fall on a narrow slot (AB) in an opaque barrier, the direction of propagation of which is perpendicular to the surface of the slot (Fig. Let us demonstrate this by calculating the diffraction of light by a slit. However, in a number of cases with a high degree of symmetry, the amplitude of the resulting oscillations can be found by algebraic or geometric summation. Emission of secondary waves by wave surface elementsĬalculations related to the application of the Huygens-Fresnel principle, in the general case, are a complex mathematical problem. The amplitude of each secondary wave is proportional to the area of the element dS, inversely proportional to the distance r to the point O, and decreases with increasing angle αīetween normal n to the element dS and direction to the point O (Fig. ![]() According to the Huygens-Fresnel principle the magnitude of light oscillations at some point O is the result of interference at this point of coherent secondary waves emitted everyone wave surface elements. ![]() The Huygens principle supplemented in this way is called the Huygens-Fresnel principle.Ģ. This drawback was eliminated by Fresnel, who supplemented the Huygens principle with the concept of the interference of secondary waves and their amplitudes. Huygens' principle says nothing about the intensity of the secondary waves. The figure shows that the envelope of these waves penetrates into the region of the geometric shadow, the boundaries of which are marked with a dashed line. Explanation of Huygens' principleĮach point of the wave front emitted by the hole serves as the center of secondary spherical waves. Let a plane wave fall on a barrier with a hole, the front of which is parallel to the barrier (Fig. Let us explain the application of the Huygens principle by the following example. The envelope of these waves gives the position of the wave front at the next moment in time. According to Huygens principle, each point of the wave front is the center of coherent secondary waves. Huygens-Fresnel principleĭiffraction of light called a complex of phenomena that are due to its wave nature and are observed during the propagation of light in a medium with sharp inhomogeneities.Ī qualitative explanation of diffraction is given by Huygens principle, which establishes the method of constructing the wave front at time t + Δt if its position at time t is known.ġ. The relatively late discovery of light diffraction (16th-17th centuries) is connected with the smallness of the lengths of visible light.Ģ1.1. (Diffraction does not only show up for light.)ĭiffraction is a wave phenomenon that is most clearly manifested when the dimensions of the obstacle are commensurate (of the same order) with the wavelength of light. In phenomena associated with diffraction, there is a significant deviation of the behavior of light from the laws of geometric optics. In a narrow but most commonly used sense, light diffraction is the rounding of light rays around the boundaries of opaque bodies, the penetration of light into the region of a geometric shadow. Characteristics of a diffraction grating as a spectral device.ħ. Diffraction of light by a slit in parallel beams.ĥ. ![]()
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