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Diffraction ○｜Definition｜1st｜20260911124749-00-⌔
Diffraction
Diffraction is the deviation of waves from straight-line propagation due to an obstacle or through an aperture, without any change in their energy. Diffraction is the same physical effect as interference, but interference is typically used for the superposition of a few waves, while the term diffraction is used when many waves are superposed.1 The term diffraction pattern is used to refer to an image or map of the different directions of the waves after they have been diffracted. Diffraction patterns are pronounced when a wave from a coherent source (such as a laser) encounters a slit/aperture as shown in the first image.
In classical physics, diffraction is described by the Huygens–Fresnel principle that treats each point in a propagating wavefront as a collection of individual spherical wavelets.2 The patterns are due to the summation over different points on the wavefront (or, equivalently, each wavelet) that travel by paths of different lengths to the registering surface. If there are multiple closely spaced openings, a complex pattern of varying intensity can result. Other types of apertures or obstacles lead to different patterns, some of which are described later on this page.
These effects occur when a light wave travels through a medium with a varying refractive index, or when a sound wave travels through a medium with varying acoustic impedance – all waves diffract,3 including gravitational waves,4 water waves, and other electromagnetic waves such as X-rays, radio waves as well as matter waves such as electrons and neutrons. It plays a role in many areas, ranging from security devices on credit cards to methods of determining the atomic structure of materials at the nanoscale.
Italian scientist Francesco Maria Grimaldi coined the word diffraction and was the first to record accurate observations of the phenomenon in 1660. After that various equivalent formulations were derived; mathematically, diffraction is explained by solving the wave equation for electromagnetic waves, or Schroedinger’s equation for matter waves, in some cases with relativistic corrections.
Printed 2026-09-11.
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Link to original Footnotes
Hecht, Eugene (2002). Optics (4th ed.). United States of America: Addison Wesley. ISBN 978-0-8053-8566-3. ↩
Wireless Communications: Principles and Practice, Prentice Hall communications engineering and emerging technologies series, T. S. Rappaport, Prentice Hall, 2002 pg 126 ↩
Suryanarayana, C.; Norton, M. Grant (29 June 2013). X-Ray Diffraction: A Practical Approach. Springer Science & Business Media. p. 14. ISBN 978-1-4899-0148-4. Retrieved 7 January 2023. ↩
Kokkotas, Kostas D. (2003). “Gravitational Wave Physics”. Encyclopedia of Physical Science and Technology. pp. 67–85. doi:10.1016/B0-12-227410-5/00300-8. ISBN 978-0-12-227410-7. ↩
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