Extinction (optics)
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.
With the incident radiation and the exiting radiation, the extinction describes the reciprocal value of the transmittance as a logarithmic quantity :
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.
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
- ↑ DIN 1349: Transmission of optical radiation through media. Optically clear materials, sizes, symbols and units.
- ^ 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]).