Why scattering occurs

When clouds become very deep, less and less of the incoming solar radiation makes it through to the bottom of the cloud, which gives these clouds a darker appearance. Terms for using data resources. CD-ROM available. Debye or Mie is an elastic scattering mechanism which occurs from relatively large particles or molecules with dimensions comparable with the wavelength of the incident radiation, or larger, and the resulting scattered radiation is non-uniform.

The effect is not very wavelength dependent. This process gives rise to the white scattered light seen in clouds or fog. Brillouin scattering is an inelastic scattering mechanism which typically occurs in light scattering from solid materials. The incident radiation wavelength is modified by the energy levels of sound waves or Phonons in the solid material which is typically very small shifts. Raman is an inelastic scattering mechanism where the frequency of the scattered radiation is changed by the gain or loss of energy which corresponds to energy levels in an atom or molecule.

The process is used for many forms of diagnostic analysis. Raman scattering is very weak and is typically much smaller than the Rayleigh scattered light, so great care must be taken extract the Raman signal from the Rayleigh signal, particularly for small frequency shifts.

For detail please see this Raman application note. Index of Refraction n : When light is transmitted through a material, each photon travels at the speed of light, c. However, Rayleigh scattering causes the transmitted wave to be out of phase with the free-space initial wave. The light is scattered many times as it travels through the medium. Each time the light is scattered, the scattering causes a phase shift. This translates to a change in the phase velocity within the medium, of the beam from c.

Note: this box searches only for keywords in the titles of encyclopedia articles. For full-text searches on the whole website, use our search page. Note: the article keyword search field and some other of the site's functionality would require Javascript, which however is turned off in your browser. In various situations, light can be scattered, i. The term scattering is mostly used for diffuse scattering , where light is sent into a wide range of directions.

A classical example is scattering of light at a rough surface, having a microscopically irregular structure. However, there are also cases with stimulated scattering , where the direction of scattered light is determined by some incident light. This article describes various physical mechanisms which occur in the context of scattering of light. Rayleigh scattering , named after Lord Rayleigh, is elastic scattering of electromagnetic radiation at particles or other entities, see below which are much smaller than the wavelength of the radiation.

Elastic scattering means that the wavelength of the scattered light is not changed, apart from a possible Doppler shift due to the movement. That implies that the inner energy of the scattering particles is not changed; there is no electronic excitation or deexcitation involved, for example. The process can be described such that the particles scattering centers experience an oscillating polarization due to the light, and that polarization leads to radiation of light in all directions.

At the same time, the incident light is attenuated accordingly. The intensity of scattering scales with the fourth power of the optical frequency , or with the inverse fourth power of the wavelength. This results from the basic properties of dipole radiation.

This means that forward and backward scattering are stronger than scattering to transverse directions. That can be understood by considering that the induced dipoles oscillate in directions perpendicular to the propagation direction of the incident light, and that they cannot radiate along the direction of oscillation.