Laser diffraction experiments can be conducted using an optical bench, as shown below. Light from the laser (of wavelength λ) is diffracted by a mask (usually a small aperture or grating) and projected onto the screen, located at a large distance away, such that Fraunhofer geometry applies. The light on the screen is known as the diffraction pattern.
The form of the diffraction pattern from a single slit mask, of width w, involves the mathematical “sinc function”, where
The observable pattern projected onto the screen (a distance L away) has an intensity pattern as follows, where x is the distance from the straight-through position:
Note that sinc(0) = 1.
Diffraction patterns can be calculated mathematically. The operation that directly predicts the amplitude of the diffraction pattern from the mask is known as a Fourier Transform (provided the conditions for Fraunhofer Diffraction are satisfied). The derivation of some simple patterns can be found here.
A diffraction grating is effectively a multitude of equally-spaced slits. The diffraction pattern from a complex mask such as a grating can be constructed from simplier patterns via the convolution theorem. The observed diffraction pattern is composed of repeated "sinc-squared" functions. Their positions from the central spot are determined by s (the spacing between slits) and their relative intensity is dependent on w (the width of individual slits).
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