Absorption (electromagnetic Radiation) - Quantifying Absorption

Quantifying Absorption

There are a number of ways to quantify how quickly and effectively radiation is absorbed in a certain medium, for example:

• The absorption coefficient, and some closely related derived quantities:
  • The attenuation coefficient, which is sometimes but not always synonymous with the absorption coefficient
  • Molar absorptivity, also called "molar extinction coefficient", which is the absorption coefficient divided by molarity (see also Beer–Lambert law).
  • The mass attenuation coefficient, also called "mass extinction coefficient", which is the absorption coefficient divided by density (see also mass attenuation coefficient).
  • The absorption cross section and scattering cross-section are closely related to the absorption and attenuation coefficients, respectively.
  • "Extinction" in astronomy is equivalent to the attenuation coefficient.
• Penetration depth and skin effect,
• Propagation constant, attenuation constant, phase constant, and complex wavenumber,
• Complex refractive index and extinction coefficient,
• Complex dielectric constant,
• Electrical resistivity and conductivity.
• Absorbance (also called "optical density") and optical depth (also called "optical thickness") are two related measures of the total light-blocking power of a certain medium with a certain thickness.
• Percentage of the incoming light which gets absorbed.

All these quantities measure, at least to some extent, how well a medium absorbs radiation. However, practitioners of different fields and techniques tend to conventionally use different quantities drawn from the list above. It is, however, easy to convert from one measure to another, see Mathematical descriptions of opacity.