Topics in Particle and Dispersion Science

Attenuation of light: Effect of multiple scattering

Parent topic

 
Fig. 3. Schematic illustration of the effect of elastic multiple scattering on transmission of light through a medium. The white arrows symbolically represent the photon paths. A path should not be interpreted as a localized photon trajectory because photons of a plane wave have infinite extent in a direction orthogonal to the propagation direction. Fly the mouse over a path link in the text below to show the relevant path alone. The source (S) is unidirectional and the detector (D) is sensitive only to radiation incident along a direction indicated by white arrows emerging from S.

In the case of multiple scattering, the probability of re-scattering of a previously scattered photon cannot be neglected. The contribution of q-times scattered photons to the scattered light power decays as p(ξ₀, ξ₁) × p(ξ₁, ξ₂) × ... × p(ξ_q-1, ξ_q), where p(ξ_i-1, ξ_i) is the value of the phase function for the photon incident from direction ξ_i-1 and scattered in direction ξ_i. In a multiple-scattering medium, few photons reach the detector via paths that do not involve scattering events (path 1). Photons arriving at the detector may do so along paths that involve one or more scattering events (path 2, path 3, path 5). However, if the photon approaches the detector from a direction outside of the range of acceptable directions, it does not contribute to the detector output (for example, path 2 and path 3), hence the last legs of such paths are differentiated from the others by making them dashed. In natural media (for example, seawater) and other media where the probability of scattering the visible light at near-forward directions is much higher than that at any other direction, the path of a photon generally deviates little (for example, path 2, path 5) and scattering at large angles (path 6) is infrequent. Note that with multiple scattering, some scattered photons may arrive at the detector along a direction (path 5) which is the same as the beam direction. Hence, they cannot be discriminated against based on the direction of propagation as can be done for scattered light that approaches the detector from other directions (see Acceptance angle of the detector). See also effects of absorption and single scattering on transmission of light by a medium.

CITATION: Swanson N. L., Jonasz M. 2007. Attenuation of light: Contributing processes - effect of multiple scattering (www.tpdsci.com/Tpc/AtnCtbFigMSca.php). In: Top. Part. Disp. Sci. (www.tpdsci.com).

HISTORY: Published: 21-Nov-2007 Modified: 04-Jun-2010 Peer-reviewed: 22-Dec-2007

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