This article is about dispersion of waves in optics. Optics and refraction pdf compact fluorescent lamp seen through an Amici prism. In optics, dispersion is the phenomenon in which the phase velocity of a wave depends on its frequency. Media having this common property may be termed dispersive media.
Sometimes the term chromatic dispersion is used for specificity. In optics, one important and familiar consequence of dispersion is the change in the angle of refraction of different colors of light, as seen in the spectrum produced by a dispersive prism and in chromatic aberration of lenses. Most often, chromatic dispersion refers to bulk material dispersion, that is, the change in refractive index with optical frequency. However, in a waveguide there is also the phenomenon of waveguide dispersion, in which case a wave’s phase velocity in a structure depends on its frequency simply due to the structure’s geometry.
The variation of refractive index vs. The wavelengths of visible light are shaded in grey. Material dispersion can be a desirable or undesirable effect in optical applications. The dispersion of light by glass prisms is used to construct spectrometers and spectroradiometers. Holographic gratings are also used, as they allow more accurate discrimination of wavelengths.
The most commonly seen consequence of dispersion in optics is the separation of white light into a color spectrum by a prism. In this case, the medium is said to have normal dispersion. Thus, blue light, with a higher refractive index, will be bent more strongly than red light, resulting in the well-known rainbow pattern. Another consequence of dispersion manifests itself as a temporal effect. The group velocity vg is often thought of as the velocity at which energy or information is conveyed along the wave.
In most cases this is true, and the group velocity can be thought of as the signal velocity of the waveform. The group velocity itself is usually a function of the wave’s frequency. If D is less than zero, the medium is said to have positive dispersion. If D is greater than zero, the medium has negative dispersion.