See also: Absorption

The Optical absorption in , or electromagnetism, indicates a physical process by which the electromagnetic energy is transformed into another form of energy.

Microscopic level

On the level of the photons (quanta of light), the absorption represents the phenomenon by which the energy of a photon is taken by another particle, for example an atom from which the electrons of valence carry out a transition between 2 energy levels electronic. The photon is then destroyed by the operation, electromagnetic energy is absorbed and transformed into electronic energy. This absorptive energy can thereafter be Re-transform in electromagnetic energy by the emission of photon (S), or be transformed into particulate agitation (increase the speed of the particle) what is translated at the macroscopic level by an increase in the temperature (electromagnetic energy was transformed into heat).

See Spectroscopy and electromagnetic Spectrum.

Macroscopic level

On the level of traditional electromagnetism, the absorption constitutes the phenomenon by which any material attenuates any electromagnetic wave the beam (it is the macroscopic consequence of the preceding paragraph), absorptive energy is then converted into heat (Joule effect). Each material has clean index properties - from one material to another of electromagnetic absorption according to the wavelength, which are noted by the imaginary part of its Permittivité and its permeability.

To note that the phenomenon of absortion is connected to the phenomenon of Dispersion by Relations of Kramers-Krönig.

Practical aspect

For the majority of the substances, the rate of absorption varies with the wavelength of the incidental light, driving with the appearance of Couleur in the pigments which absorb certain wavelengths but not others. For example, with an incidental white light, an object which absorbs the wavelengths in blue, green and yellow, will appear of red color. A material of black color thus absorbs all the wavelengths (converted into heat), whereas a material of white color reflects them.

Internal bonds

• Law of Beer-Lambert