## Definition and units of scattering coefficient## µ
| ECE532 Biomedical Optics ©1998 Steven L. Jacques, Scott A. Prahl Oregon Graduate Institute |

Consider a scattering particle idealized as a sphere with a particular geometrical size. Consider that this sphere redirects incident photons into new directions and so prevents the forward on-axis transmission of photons, thereby casting a shadow. This process constitutes scattering. This description is of course an oversimplified and schematicized version of the real situation. However, it does provide a simple concept which captures the essence of the **scattering coefficient**, a parameter analogous to the absorption coefficient discussed previously.

The size of the scattering shadow is called the **effective cross-section** (_{s} [cm^{2}]) and can be smaller or larger than the geometrical size of the scattering particle (A [cm^{2}]), related by the proportionality constant called the **scattering efficiency** Q_{s} [dimensionless]:

The **scattering coefficient** µ_{s} [cm^{-1}] describes a medium containing many scattering particles at a concentration described as a **volume density** _{s} [cm^{3}]. The scattering coefficient is essentially the cross-sectional area per unit volume of medium.

Experimentally, the units [cm^{-1}] for µ_{s} are inverse length, such that the product µ_{s}L is dimensionless, where L [cm] is a photon's pathlength of travel through the medium. The probability of transmission T of the photon without redirection by scattering after a pathlength L is:

**
to next page |
3. Optical Properties |
**
ECE 532 |
OGI Optics Courses |
OMLC homepage.