Fr.: dispersion angulaire
The rate of change of the angles of emergence θ of various wavelengths from a dispersing prism: dθ/dλ.
→ angular; → dispersion.
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.
→ anomalous; → dispersion.
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.
→ atmospheric; → dispersion.
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.
→ cross; → dispersion.
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.
→ dispersion; → curve.
Fr.: équation de dispersion
An equation representing the variation of → refractive index as a function of → wavelength; for example → Cauchy's equation and → Sellmeier's equation.
→ dispersion; → equation.
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.
→ dispersion; → measure.
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.
→ dispersion; → relation.
Fr.: dispersion normale
The dispersion in which a shorter wavelength is associated with a higher → refractive index. Contrasted with the → anomalous dispersion.
→ normal; → dispersion.
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.
→ pre-; → dispersion.
Fr.: dispersion spectrale
→ spectral; → dispersion.
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.
→ velocity; → dispersion.