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. These secondary maxima are however the periodically repeating counterparts of the central one, and are not the bumps you would see with a finite grating.1. The secondary maxima of a single slit are due to the fact that the spacing between slits is nil. You might also be interested in knowing that a single slit pattern is the diffraction pattern of a diffraction grating, in the limit that the number of gratings goes to infinity, so a single slit diffraction pattern gives you an idea of the infinite grating pattern. If the line starts from the center of your grating, this is of course true, but if it does not, then your calculation is no longer valid due to the finiteness of your grating. You can draw a perpendicular from your grating to the screen, and the calculation for the maximum will still be true for the point where the perpendicular intersects your screen, but only if you have the same number of slits to the left of the line as you do to to the right of the line. A simplifying assumption is made when calculating the path difference for multiple slits: you only look at two neighboring slits. If you had an infinitely long grating, you should be able to do away with the bumps. These bumps arise when not every single slit in the grating are in phase - some are, but others aren't, so you can't recover max intensity. The intensity profile when you have more than 2 slits has some additional bumps here and there, which have less intensity than the central maximum, but these will not appear in double slit diffraction. I don't mean the periodic repeating of the maximum intensity, which Young's slits show as well. But the intensity profile changes with the number of slits.īut there are several additional bumps in intensity when you have more than two slits, that aren't the maxima. The equation for the wavelengths for the central maximum is the same, because it's pretty much just geometry. If you take the intensity profile for n slits (a diffraction grating) and set n = 2 you'll recover Young's double slit intensity profile. The double slit is just diffraction grating with two slits instead of several. Young's double slit experiment and the diffraction grating are the same thing.
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