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.
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