Fr.: dispersion angulaire
The rate of change of the angles of emergence θ of various wavelengths from a dispersing prism: dθ/dλ.
Fr.: dispesrion anormale
The phenomenon whereby the → refractive index of light in a medium changes rapidly with wavelength in the vicinity of an → absorption band. Hence the → dispersion curve of the substance shows marked deviations from → Cauchy's equation, in contrast with the behavior of → normal dispersion. On the shorter λ side of the absorption band the refractive index falls off more rapidly than required by Cauchy's equation representing values of n for visible light. On the long λ side of the absorption band the index is very high, decreasing at first rapidly and then more slowly as one goes beyond the absorption band.
Fr.: dispersion atmosphérique
The splitting of starlight into a spectrum in the atmosphere because the atmosphere acts as a refracting prism. This phenomenon brings about a practical problem for spectroscopic observations using a slit. → differential refraction; → atmospheric refraction.
pâšeš-e calipâyi, ~ xâji
Fr.: dispersion croisée
Dispersion of a light beam by using two dispersing elements (grating, grism), one for separating spectral orders, the other for resolving spectral features within an order.
1) The resolution of white light into its component wavelengths,
either by → refraction or by → diffraction.
Dispersion is actually an effect in which radiations having → different
wavelengths travel at different speeds in the medium. Since
the → angle of refraction
of each radiation vary as a function of
its → wavelength, the component waves deviate from each other.
Verbal noun of → disperse.
Fr.: courbe de dispersion
A graph displaying the variation of the → refractive index of a substance against the wavelength of the electromagnetic wave passing through the substance.
Fr.: équation de dispersion
Fr.: mesure de dispersion
A parameter used in radio astronomy which describes the amount of dispersion in a radio signal due to its passage through an intervening plasma. It is proportional to the product of the interstellar electron density and the distance to the source.
Fr.: relation de dispersion
An equation that describes how the → angular frequency, ω, of a wave depends on its → wave number, k. For the simplest of waves, where the speed of propagation, c, is a constant, ω(k) = ck. If the → phase velocity depends on k, that is for a dispersive medium, the function ω(k) is nonlinear.
Fr.: dispersion normale
A technique in spectroscopy which uses a combination of several dispersive elements (prisms in series or a grism) before focusing the light on the primary disperser, usually a grating, in order to achieve high spectral resolutions.
Fr.: dispersion spectrale
Fr.: dispersion de vitesses
The → standard deviation of a velocity → distribution. It indicates how objects of the sample move relative to one another. Objects with similar velocities have a small velocity dispersion, whereas objects with very different velocities have a large velocity dispersion.