The double slit diffraction experiment explores the optical interference phenomena discovered by Thomas Young. The light source is an imaginary coherent laser that is tunable over the entire visible wavelength spectrum. This tutorial can be adjusted by changing the wavelength with the slider on the left, and/or changing the distances between the two slits with the slider on the right.

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In this experiment, visible monochromatic light is diffracted through a screen with two adjustable slits. As the light waves spread out from the slit, they meet which results in interference between the two waves. If the waves are in phase with each other they will add together, resulting in constructive interference. However, where the waves are out of phase with each other they will subtract amplitude from each other, which results in destructive interference. The intensity of the interference is displayed at the bottom of the tutorial both as a two-dimensional graph of intensity versus diffraction angle and as a representation of how the light intensities would appear on a screen.

In this experiment, the location of bright fringes is given by the equation:

where j_m is the angle of a fringe of the order m. The central bright fringe located at j = 0 corresponds to m=0 and is called the zeroth-order maximum. The two bright fringes on either side of the central bright fringe correspond to m=1, and are called the first-order maxima, and so on.