What is an extinction coefficient?

In chemistry and biology, the extinction coefficient can refer to the mass attenuation coefficient or the molar absorptivity, which both relate to calculations of how different substances absorb light wavelengths. In physics, the extinction coefficient relates to index of refraction and absorption and is based on intensity and electric field.

When used in physics, the extinction coefficient may also be called the absorption coefficient and is used in calculations for the plane wave. When used as the mass attenuation coefficient, the extinction coefficient is represented by the Greek letter mu and is calculated in relation with Euler's number and the changing intensity of a beam of light.