Wave vector

A vector that points along a wave’s direction of propagation and has magnitude equal to its angular spatial frequency, measured in radians per unit distance.

Wavenumber: A scalar spatial frequency equal to the magnitude of a wave vector, commonly expressed in radians per unit distance. It is the wave vector’s magnitude and sets the rate of phase change along propagation.
Spatial frequency: The rate at which a pattern repeats across space, usually measured in cycles or radians per unit distance. Wave vector magnitude is the angular form of spatial frequency.
Snell's law: A relation describing how a wave’s direction changes when it crosses a boundary between media. Conservation of the wave vector component parallel to an interface yields refraction angles.
Propagation constant: A generally complex quantity describing how a wave’s amplitude and phase change along a propagation path. Unlike a wave vector, it can include attenuation as well as phase change.
Wavelength: The spatial period of a wave: the distance over which its pattern repeats. Its reciprocal, multiplied by 2π, gives the wave vector’s magnitude.
Vector (mathematics and physics): A quantity with magnitude and direction, represented by components in a coordinate system. Its vector structure separates propagation direction from spatial frequency.
Bragg's law: A condition for constructive scattering of waves by regularly spaced planes in a material. Diffraction conditions can be expressed as changes in wave vector matching reciprocal-lattice vectors.
Poynting vector: A vector giving the directional energy flux density of an electromagnetic field. It describes energy transport, which need not point along the wave vector in every medium.
Phase: A quantity specifying a wave’s position within its cycle at a given place and time. The wave vector determines how phase changes with position.
Periodic function: A function that repeats its values at regular intervals in one or more variables. A wave vector describes the spatial periodicity of a repeating wave pattern.

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