There are a few things that struck my attention about the “Duplicate” Program and manual there are reminders about the importance of having aīackup in case something unforeseen happens. 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. Since light is an electromagnetic wave, its wavefront is altered much like a water wave encountering an obstruction. This diffraction phenomenon occurs because of interference (see Laser Light Characteristics on coherence for details) between different portions of the wavefront. The resulting intensity distribution is called a diffraction pattern. 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. These directions are strongly dependent on both the slit spacing and wavelength of the incident light. It provides angular dispersion, i.e., the ability to separate wavelengths based on the angle that they emerge from the grating.Ĭonsequently, 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. Gratings can be transmissive, like the multi-slit aperture, but they can also be reflective where the grooved surface is overcoated with a reflecting material such as aluminum. A typical diffraction grating (see Figure 2) consists of a large number of parallel grooves (representing the slits) with a groove spacing (denoted d G, also called the pitch) on the order of the wavelength of light. This is more commonly reported as the groove density ( G), which is the reciprocal of d G, e.g., typical gratings have G values between grooves per mm.
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