Extinction (optics)

With increasing water depth , light of different wavelengths (penetration depth ) is absorbed .

In optics , the extinction or optical density is the perceptually logarithmically formulated opacity and thus a measure of the attenuation of radiation (e.g. light ) after it has passed through a medium . It depends on the wavelength of the radiation. ${\displaystyle E}$ ${\displaystyle O}$ ${\displaystyle \lambda }$

With the incident radiation and the exiting radiation, the extinction describes the reciprocal value of the transmittance as a logarithmic quantity : ${\displaystyle I_{0}}$ ${\displaystyle I}$ ${\displaystyle \tau }$

${\displaystyle {\begin{aligned}E_{\lambda }=&\log _{10}{\frac {I_{0}}{I}}&=&\log _{10}{\frac {1}{\tau _{\lambda }}}=\log _{10}{O_{\lambda }}\\=&-\log _{10}{\frac {I}{I_{0}}}&=&-\log _{10}{\tau _{\lambda }}\end{aligned}}}$

The definition of extinction using the natural logarithm is particularly found in physics . In astronomy , the extinction is given in size classes . The physical quantity diabatia takes into account the exponential increase in extinction with the layer thickness of the irradiated material by forming a further logarithm.

The processes of absorption , scattering , diffraction and reflection are generally involved in the attenuation . In analytical applications, see Beer-Lambert law , scattering and diffraction are often insignificant and the reflection losses are empty or parallel measurement in taken into account. Then, instead of extinction of ( decadic ) absorbance (Engl. Absorbance , absorptivity or spectrophotometric absorbance () standard- compliant designation) spoken. As a criticism it should be mentioned that the reduction to the intensity does not take into account the wave properties of light. Therefore, the extinction is generally non-linearly dependent on the path length and the concentration. ${\displaystyle I_{0}}$

The substance-specific strength of the attenuation related to the path length is indicated with the extinction coefficient and the absorption coefficient . If the wave nature of the light is taken into account, the result is that the coefficients are not material-specific, but depend on boundary conditions such as the surrounding medium, shape and heterogeneity of the material, etc.

Individual evidence

1. ↑ DIN 1349: Transmission of optical radiation through media. Optically clear materials, sizes, symbols and units.
2. ^ ^{A b} Thomas Günter Mayerhöfer, Susanne Pahlow, Jürgen Popp: The Bouguer-Beer-Lambert law: Shining light on the obscure . In: ChemPhysChem . n / a, n / a, July 14, 2020, ISSN  1439-4235 , doi : 10.1002 / cphc.202000464 ( wiley.com [accessed July 19, 2020]).