13.8: Double-Slit Interference and Diffraction Gratings

Describe the behavior of a wave and the resulting diffraction pattern resulting from a wave passing through multiple openings.

13.8.A.1 The pattern of intensity resulting from a wave interacting with a double slit is the combination of wave diffraction and wave interference.

13.8.A.1.i When only considering wave interference, a double slit creates a pattern of uniformly spaced maxima.
13.8.A.1.ii The local maxima of an interference pattern can be calculated with the following equation, where y is the distance between the mth bright line and the central maxima as viewed on a screen a distance D from the slits, and d is the distance between the two slits.
13.8.A.1.iii When considering wave interference and wave diffraction, a double slit creates a diffraction pattern of maxima and minima superimposed within the envelope created by single-slit diffraction.

Young’s double-slit experiment

Investigate the

13.8.A.2 Interference patterns produced by light interacting with a double slit indicate light has wave properties. This is sometimes called Young’s double-slit experiment.

13.8.A.3 Visual representations of double-slit diffraction patterns are useful in determining the physical properties of the slits and the interacting waves.

13.8.A.4 A diffraction grating is a collection of evenly spaced parallel slits or openings that produces an interference pattern that is the combination of numerous diffraction patterns superimposed on each other.

A diffraction grating is essentially a multi-slit surface. It provides angular dispersion, i.e., the ability to separate wavelengths based on the angle that they emerge from the grating. 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.

13.8.A.5 When white light is incident on a diffraction grating, the center maximum is white, and the higher-order maxima disperse white light into a rainbow of colors with the longest wavelength light (red) appearing farthest from the central maximum.