page_title: Fraunhofer diffraction
section_title: Diffraction by a rectangular aperture
hierarchical_section_title: Fraunhofer diffraction / Examples of Fraunhofer diffraction / Diffraction by a rectangular aperture
caption_attribution_description: English: Square diffraction.jpg, which is a public domain image by user:V81. I have stretched it so it represnet rectnagular diffraction.
context_page_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.
  The equation was named in honor of Joseph von Fraunhofer although he was not actually involved in the development of the theory.
  A detailed mathematical treatment of Fraunhofer diffraction is given in Fraunhofer diffraction equation.
context_section_description: The form of the diffraction pattern given by a rectangular aperture is shown in the figure on the right (or above, in tablet format). There is a central semi-rectangular peak, with a series of horizontal and vertical fringes.  The dimensions of the central band are related to the dimensions of the slit by the same relationship as for a single slit so that the larger dimension in the diffracted image corresponds to the smaller dimension in the slit.  The spacing of the fringes is also inversely proportional to the slit dimension.
  If the illuminating beam does not illuminate the whole vertical length of the slit, the spacing of the vertical fringes is determined by the dimensions of the illuminating beam.  Close examination of the double-slit diffraction pattern below shows that there are very fine horizontal diffraction fringes above and below the main spot, as well as the more obvious horizontal fringes.
caption: Computer simulation of Fraunhofer diffraction by a rectangular aperture
exif: {}