Mathematical Descriptions of Opacity - Absorption Coefficient

One way to incorporate attenuation into the mathematical description of the wave is via an absorption coefficient:

where is the absorption coefficient. The intensity in this case satisfies:

i.e.,

The absorption coefficient, in turn, is simply related to several other quantities:

• Attenuation coefficient is essentially (but not quite always) synonymous with absorption coefficient; see attenuation coefficient for details.
• Molar absorption coefficient or Molar extinction coefficient, also called molar absorptivity, is the absorption coefficient divided by molarity (and usually multiplied by ln(10), i.e., decadic); see Beer-Lambert law and molar absorptivity for details.
• Mass attenuation coefficient, also called mass extinction coefficient, is the absorption coefficient divided by density; see mass attenuation coefficient for details.
• Absorption cross section and scattering cross section are both quantitatively related to the absorption coefficient (or attenuation coefficient); see absorption cross section and scattering cross section for details.
• The absorption coefficient is also sometimes called opacity; see opacity (optics).