![]() It provides angular dispersion, i.e., the ability to separate wavelengths based on the angle that they emerge from the grating. Consequently, surfaces with well-defined slit locations can be used to direct light of certain wavelengths into specific directions.Ī diffraction grating is essentially a multi-slit surface. These directions are strongly dependent on both the slit spacing and wavelength of the incident light. Similarly, when light passes through an opaque screen consisting of multiple elongated apertures (or slits) with a fixed spacing between them, the emerging wavefronts constructively interfere to produce a diffraction pattern with intensities peaked in certain directions as shown in Figure 1. The resulting intensity distribution is called a diffraction pattern. This diffraction phenomenon occurs because of interference (see Laser Light Characteristics on coherence for details) between different portions of the wavefront. Since light is an electromagnetic wave, its wavefront is altered much like a water wave encountering an obstruction. When light encounters an obstacle such as an opaque screen with a small opening (or aperture), the intensity distribution behind the screen can look much different than the shape of the aperture that it passed through. Textbook content produced by OpenStax is licensed under a Creative Commons Attribution License. Use the information below to generate a citation. Then you must include on every digital page view the following attribution: If you are redistributing all or part of this book in a digital format, Then you must include on every physical page the following attribution: If you are redistributing all or part of this book in a print format, Want to cite, share, or modify this book? This book uses the A range of diffraction gratings are available for selecting wavelengths for such use. Another vital use is in optical fiber technologies where fibers are designed to provide optimum performance at specific wavelengths. A diffraction grating can be chosen to specifically analyze a wavelength emitted by molecules in diseased cells in a biopsy sample or to help excite strategic molecules in the sample with a selected wavelength of light. Diffraction gratings are key components of monochromators used, for example, in optical imaging of particular wavelengths from biological or medical samples. That is, their bright fringes are narrower and brighter while their dark regions are darker. What makes them particularly useful is the fact that they form a sharper pattern than double slits do. Where are diffraction gratings used in applications? Diffraction gratings are commonly used for spectroscopic dispersion and analysis of light. (credit a: modification of work by "Opals-On-Black"/Flickr credit b: modification of work by “whologwhy”/Flickr) Applications of Diffraction Gratings What remains are only the principal maxima, now very bright and very narrow ( Figure 4.12).įigure 4.15 (a) This Australian opal and (b) butterfly wings have rows of reflectors that act like reflection gratings, reflecting different colors at different angles. Furthermore, because the intensity of the secondary maxima is proportional to 1 / N 2 1 / N 2, it approaches zero so that the secondary maxima are no longer seen. This makes the spacing between the fringes, and therefore the width of the maxima, infinitesimally small. We can see there will be an infinite number of secondary maxima that appear, and an infinite number of dark fringes between them. Recall that N – 2 N – 2 secondary maxima appear between the principal maxima. The analysis of multi-slit interference in Interference allows us to consider what happens when the number of slits N approaches infinity. Diffraction Gratings: An Infinite Number of Slits The key optical element is called a diffraction grating, an important tool in optical analysis. ![]() However, most modern-day applications of slit interference use not just two slits but many, approaching infinity for practical purposes. ![]() ![]() Discuss the pattern obtained from diffraction gratingsĪnalyzing the interference of light passing through two slits lays out the theoretical framework of interference and gives us a historical insight into Thomas Young’s experiments.By the end of this section, you will be able to: ![]()
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