Airy disk

The central bright region of the diffraction pattern produced by a circular aperture, surrounded by progressively fainter rings. Its angular size sets a fundamental diffraction limit on optical resolution.

Fraunhofer diffraction: The far-field diffraction pattern produced when waves pass through an aperture or around an obstacle. The Airy disk is the circular-aperture case of this far-field pattern.
Diffraction: The spreading and interference of waves as they pass through openings or encounter obstacles. The Airy disk is a characteristic diffraction effect of a circular opening.
Optical resolution: The ability of an optical system to distinguish nearby features as separate. The disk’s size limits how closely two point sources can be distinguished.
Gaussian beam: A beam whose transverse intensity profile follows a Gaussian distribution and whose wavefront has a Gaussian-beam form. Its ideal focused spot has a Gaussian profile, unlike the rings of a circular-aperture Airy pattern.
Circular aperture: An opening with a circular boundary that transmits waves or light. Its rotational symmetry produces the concentric rings of the Airy pattern.
Huygens–Fresnel principle: A wave-propagation principle in which each point on a wavefront acts as a source of secondary wavelets. Interference among wavelets across the aperture forms the disk and its rings.
Abbe diffraction limit: A resolution bound for microscopy that relates the smallest distinguishable detail to wavelength and numerical aperture. It describes the same wave-optical constraint that broadens a point into an Airy disk.
Sinc function: A function proportional to the sine of its argument divided by that argument, with a central peak and diminishing oscillations. A one-dimensional slit produces a sinc-squared intensity profile rather than the Airy pattern.
Bessel function: A solution of Bessel’s differential equation, commonly used to describe radial wave phenomena. The Airy pattern’s intensity profile is expressed using a first-order Bessel function.
Wavelength: The distance between successive corresponding points on a wave, such as adjacent crests. The Airy disk’s angular radius increases in proportion to wavelength.

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