Wavefront

In physics, the wavefront of a time-varying <a href="/facts/Wave/fU0HH6St">wave</a> <a href="/facts/Field_(physics)/FJdAKeRA">field</a> is the set (<a href="/facts/Locus_(mathematics)/t4swdGJq">locus</a>) of all <a href="/facts/Point_(geometry)/6YPAvX2a">points</a> having the same <a href="/facts/Phase_(waves)/cpGtuVll">phase</a>. The term is generally meaningful only for fields that, at each point, vary <a href="/facts/Sinusoidally/mD1CB09M">sinusoidally</a> in time with a single temporal frequency (otherwise the phase is not well defined).
Wavefronts usually move with time. For waves propagating in a <a href="/facts/Dimension_(mathematics)/0ktmUyac">unidimensional</a> medium, the wavefronts are usually single points; they are <a href="/facts/Curve/xBQ0pTBW">curves</a> in a two dimensional medium, and <a href="/facts/Surface_(mathematics)/whF08jvy">surfaces</a> in a three-dimensional one.

For a <a href="/facts/Sinusoidal_plane_wave/BGMWIa0Q">sinusoidal plane wave</a>, the wavefronts are planes perpendicular to the direction of propagation, that move in that direction together with the wave. For a sinusoidal spherical wave, the wavefronts are spherical surfaces that expand with it. If the speed of propagation is different at different points of a wavefront, the shape and/or orientation of the wavefronts may change by <a href="/facts/Refraction/S8kvSKzM">refraction</a>. In particular, <a href="/facts/Lens_(optics)/ejlH6n5c">lenses</a> can change the shape of optical wavefronts from planar to spherical, or vice versa.
In <a href="/facts/Classical_physics/gGnINVPE">classical physics</a>, the diffraction phenomenon is described by the <a href="/facts/Huygens%E2%80%93Fresnel_principle/t7lsjjA3">Huygens–Fresnel principle</a> that treats each point in a propagating wavefront as a collection of individual spherical <a href="/facts/Wavelet/3XcX4uIP">wavelets</a>. The characteristic bending pattern is most pronounced when a wave from a <a href="/facts/Coherence_(physics)/NF1Rgdoa">coherent</a> source (such as a laser) encounters a slit/aperture that is comparable in size to its <a href="/facts/Wavelength/kcJU0ymz">wavelength</a>, as shown in the inserted image. This is due to the addition, or <a href="/facts/Interference_(wave_propagation)/lI5f78I4">interference</a>, 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, <a href="/facts/Diffraction_grating/TUcyt7Do">closely spaced openings</a> (e.g., a <a href="/facts/Diffraction_grating/TUcyt7Do">diffraction grating</a>), a complex pattern of varying intensity can result.

Wavefront open-in-new

Wavefront