# Fraunhofer diffraction (Diffraction by a double slit)

## Description

In optics, the Fraunhofer diffraction equation is used to model the diffraction of waves when the diffraction pattern is viewed at a long distance from the diffracting object, and also when it is viewed at the focal plane of an imaging lens. In contrast, the diffraction pattern created near the object, in the near field region, is given by the Fresnel diffraction equation.

In a diffraction by a double slit,

(Double slit fringes with sodium light illumination)
the two slits are illuminated by a single light beam. If the width of the slits is small enough (less than the wavelength of the light), the slits diffract the light into cylindrical waves. These two cylindrical wavefronts are superimposed, and the amplitude, and therefore the intensity, at any point in the combined wavefronts depends on both the magnitude and the phase of the two wavefronts.

## Variables

w_{f} | The spacing of the fringes at the given distance from the slits (mm) |

λ | The wavelength (mm) |

z | The distance from the slits (mm) |

d | The separation of the slits (mm) |