![]() In fact, each ray from the slit will have another to interfere destructively, and a minimum in intensity will occur at this angle. A ray from slightly above the center and one from slightly above the bottom will also cancel one another. Thus a ray from the center travels a distance λ/2 farther than the one on the left, arrives out of phase, and interferes destructively. In Figure 2b, the ray from the bottom travels a distance of one wavelength λ farther than the ray from the top. However, when rays travel at an angle θ relative to the original direction of the beam, each travels a different distance to a common location, and they can arrive in or out of phase. When they travel straight ahead, as in Figure 2a, they remain in phase, and a central maximum is obtained. (Each ray is perpendicular to the wavefront of a wavelet.) Assuming the screen is very far away compared with the size of the slit, rays heading toward a common destination are nearly parallel. These are like rays that start out in phase and head in all directions. According to Huygens’s principle, every part of the wavefront in the slit emits wavelets. Here we consider light coming from different parts of the same slit. The analysis of single slit diffraction is illustrated in Figure 2. In contrast, a diffraction grating produces evenly spaced lines that dim slowly on either side of center. Note that the central maximum is larger than those on either side, and that the intensity decreases rapidly on either side. ![]() ![]() Figure 1 shows a single slit diffraction pattern. Light passing through a single slit forms a diffraction pattern somewhat different from those formed by double slits or diffraction gratings. (b) The drawing shows the bright central maximum and dimmer and thinner maxima on either side. The central maximum is six times higher than shown. Monochromatic light passing through a single slit has a central maximum and many smaller and dimmer maxima on either side. Note: The small angle approximation was not used in the calculations above, but it is usually sufficiently accurate for laboratory calculations.Figure 1. Default values will be entered for unspecified parameters, but all values may be changed. The data will not be forced to be consistent until you click on a quantity to calculate. This calculation is designed to allow you to enter data and then click on the quantity you wish to calculate in the active formula above. This corresponds to a diffraction angle of θ = °. The displacement from the centerline for minimum intensity will be Enter the available measurements or model parameters and then click on the parameter you wish to calculate.ĭisplacement y = (Order m x Wavelength x Distance D)/( slit width a)įor a slit of width a = micrometers = x10^ mĪnd light wavelength λ = nm at order m = , The active formula below can be used to model the different parameters which affect diffraction through a single slit. More conceptual details about single slit diffraction With a general light source, it is possible to meet the Fraunhofer requirements with the use of a pair of lenses. ![]() The use of the laser makes it easy to meet the requirements of Fraunhofer diffraction. The diffraction pattern at the right is taken with a helium-neon laser and a narrow single slit. Fraunhofer Single Slit Diffraction Fraunhofer Single Slit
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