dispersion

The decomposition or spreading of a beam of electromagnetic radiation in relation to wavelength. A simple example is provided by the dispersion of white light into a coloured spectrum on passing through a glass prism. The light disperses because the wave velocity of light in a medium (which is reflected in the value of the refractive index of the medium) varies with wavelength. Dispersion is also used to mean a qualitative measure of the spread of a spectrum on a detector, expressed, for example, in ångströms per millimetre.