Extinction coefficient
Encyclopedia
Extinction coefficient refers to several different measures of the absorption of light in a medium:
(For the quantitative relationship between the chemistry and physics definitions, see Mathematical descriptions of opacity
.)
- In chemistry, biochemistry, molecular biology, or microbiology, the mass extinction coefficientMass attenuation coefficientThe mass attenuation coefficient is a measurement of how strongly a chemical species or substance absorbs or scatters light at a given wavelength, per unit mass...
and the molar extinction coefficientMolar absorptivityThe molar absorption coefficient, molar extinction coefficient, or molar absorptivity, is a measurement of how strongly a chemical species absorbs light at a given wavelength...
are parameters defining how strongly a substance absorbs light at a given wavelength, per mass densityDensityThe mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
or per molar concentration, respectively.
- In physics, the "extinction coefficient" is the imaginary part of the complex index of refraction, which also relates to light absorption.
(For the quantitative relationship between the chemistry and physics definitions, see Mathematical descriptions of opacity
Mathematical descriptions of opacity
When an electromagnetic wave travels through a medium in which it gets absorbed , it undergoes exponential decay as described by the Beer–Lambert law. However, there are many possible ways to characterize the wave and how quickly it is absorbed...
.)