Editing Diffraction (section)

{{Short description|Phenomenon of the motion of waves}}
{{Distinguish|text=[[refraction]], the change in direction of a wave passing from one medium to another}}
{{Use dmy dates|date=July 2022}}

[[File:Laser Interference.JPG|thumb|A [[Airy disk|diffraction pattern]] of a red [[laser]] beam projected onto a plate after passing through a small circular [[aperture]] in another plate]]
'''Diffraction''' is the deviation of [[wave]]s from straight-line propagation without any change in their energy due to an obstacle or through an [[aperture]]. The diffracting object or aperture effectively becomes a secondary source of the [[Wave propagation|propagating]] wave. Diffraction is the same physical effect as [[Wave interference|interference]], but interference is typically applied to superposition of a few waves and the term diffraction is used when many waves are superposed.<ref name="Hecht2002"/>{{rp|433}}

Italian scientist [[Francesco Maria Grimaldi]] coined the word ''diffraction'' and was the first to record accurate observations of the phenomenon in [[1660 in science|1660]].
[[File:Single Slit Diffraction.svg|thumb|upright=1.2|Infinitely many points (three shown) along length <math>d</math> project phase contributions from the [[wavefront]], producing a continuously varying intensity <math>\theta</math> on the registering plate]]

In [[classical physics]], the diffraction phenomenon is described by the [[Huygens–Fresnel principle]] that treats each point in a propagating [[wavefront]] as a collection of individual spherical [[wavelet]]s.<ref>Wireless Communications: Principles and Practice, Prentice Hall communications engineering and emerging technologies series, T. S. Rappaport, Prentice Hall, 2002 pg 126</ref> The characteristic pattern is most pronounced when a wave from a [[Coherence (physics)|coherent]] source (such as a laser) encounters a slit/aperture that is comparable in size to its [[wavelength]], as shown in the inserted image. This is due to the addition, or [[Interference (wave propagation)|interference]], of different points on the wavefront (or, equivalently, each wavelet) that travel by paths of different lengths to the registering surface. If there are multiple [[diffraction grating|closely spaced openings]], a complex pattern of varying intensity can result.

These effects also occur when a [[Electromagnetic radiation|light wave]] travels through a medium with a varying [[refractive index]], or when a [[Sound|sound wave]] travels through a medium with varying [[acoustic impedance]] – all waves diffract,<ref>{{cite book |last1=Suryanarayana |first1=C. |last2=Norton |first2=M. Grant |title=X-Ray Diffraction: A Practical Approach |date=29 June 2013 |publisher=Springer Science & Business Media |isbn=978-1-4899-0148-4 |page=14 |url=https://books.google.com/books?id=RRfrBwAAQBAJ |access-date=7 January 2023 |language=en}}</ref> including [[gravitational wave]]s,<ref>{{cite journal |last1=Kokkotas |first1=Kostas D. |title=Gravitational Wave Physics |journal=Encyclopedia of Physical Science and Technology |date=2003 |pages=67–85 |doi=10.1016/B0-12-227410-5/00300-8 |isbn=9780122274107 }}</ref> [[Wind wave|water waves]], and other [[electromagnetic radiation|electromagnetic waves]] such as [[X-ray]]s and [[radio waves]]. Furthermore, [[quantum mechanics]] also demonstrates that matter possesses [[Matter wave|wave-like properties]] and, therefore, undergoes diffraction (which is measurable at subatomic to molecular levels).<ref>{{Cite journal|last1=Juffmann|first1=Thomas|last2=Milic|first2=Adriana|last3=Müllneritsch|first3=Michael|last4=Asenbaum|first4=Peter|last5=Tsukernik|first5=Alexander|last6=Tüxen|first6=Jens|last7=Mayor|first7=Marcel|last8=Cheshnovsky|first8=Ori|last9=Arndt|first9=Markus|date=2012-03-25|title=Real-time single-molecule imaging of quantum interference|journal=Nature Nanotechnology|volume=7|issue=5|pages=297–300|doi=10.1038/nnano.2012.34|issn=1748-3395|pmid=22447163|arxiv=1402.1867|bibcode=2012NatNa...7..297J|s2cid=5918772}}</ref>