# Absorption (electromagnetic radiation) > Mediated Wiki article. Canonical URL: https://mediated.wiki/source/Absorption_(electromagnetic_radiation) > Markdown URL: https://mediated.wiki/source/Absorption_(electromagnetic_radiation).md > Source: https://en.wikipedia.org/wiki/Absorption_(electromagnetic_radiation) > Source revision: 1321659159 > License: Creative Commons Attribution-ShareAlike 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) Physical process by which matter takes up a photon's energy and stores it This article includes a list of general references, but it lacks sufficient corresponding inline citations. Please help to improve this article by introducing more precise citations. (November 2010) (Learn how and when to remove this message) An overview of absorption of [electromagnetic radiation](/source/Electromagnetic_radiation). This example shows the general principle using [visible light](/source/Visible_spectrum) as a specific example. A white [light source](/source/Light_source)—emitting light of multiple [wavelengths](/source/Wavelength)—is focused on a sample (the pairs of [complementary colors](/source/Complementary_color) are indicated by the yellow dotted lines). Upon striking the sample, [photons](/source/Photon) that match the [energy gap](/source/Energy_gap) of the [molecules](/source/Molecule) present (green light in this example) are *absorbed*, exciting the molecules. Other photons are scattered (not shown here) or transmitted unaffected; if the radiation is in the visible region (400–700 nm), the transmitted light appears as the complementary color (here red). By recording the [attenuation](/source/Attenuation) of light for various wavelengths, an [absorption spectrum](/source/Absorption_spectroscopy) can be obtained. In [physics](/source/Physics), **absorption** of [electromagnetic radiation](/source/Electromagnetic_radiation) is how [matter](/source/Matter) (typically [electrons](/source/Electrons) bound in [atoms](/source/Atom)) takes up a [photon](/source/Photon)'s [energy](/source/Energy)—and so transforms [electromagnetic energy](/source/Radiant_energy) into [internal energy](/source/Internal_energy) of the absorber (for example, [thermal energy](/source/Thermal_energy)).[1] A notable effect of the absorption of electromagnetic radiation is [attenuation](/source/Attenuation) of the radiation; attenuation is the gradual reduction of the [intensity](/source/Intensity_(physics)) of [light waves](/source/Light_waves) as they [propagate](/source/Wave_propagation) through a medium. Although the absorption of waves does not usually depend on their intensity (linear absorption), in certain conditions ([optics](/source/Optics)) the medium's transparency changes by a factor that varies as a function of wave intensity, and [saturable absorption](/source/Saturable_absorption) (or nonlinear absorption) occurs. ## Quantifying absorption Main article: [Mathematical descriptions of opacity](/source/Mathematical_descriptions_of_opacity) Many approaches can potentially quantify radiation absorption, with key examples following. - The absorption coefficient along with some closely related derived quantities - The [attenuation coefficient](/source/Attenuation_coefficient) (NB used infrequently with meaning synonymous with "absorption coefficient")[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*] - The [Molar attenuation coefficient](/source/Molar_attenuation_coefficient) (also called "molar absorptivity"), which is the absorption coefficient divided by molarity (see also [Beer–Lambert law](/source/Beer%E2%80%93Lambert_law)) - The [mass attenuation coefficient](/source/Mass_attenuation_coefficient) (also called "mass extinction coefficient"), which is the absorption coefficient divided by density - The [absorption cross section](/source/Absorption_cross_section) and [scattering cross-section](/source/Scattering_cross-section), related closely to the absorption and attenuation coefficients, respectively - ["Extinction" in astronomy](/source/Extinction_(astronomy)), which is equivalent to the attenuation coefficient - Other measures of radiation absorption, including [penetration depth](/source/Penetration_depth) and [skin effect](/source/Skin_effect), [propagation constant](/source/Propagation_constant), [attenuation constant](/source/Propagation_constant#Attenuation_constant), [phase constant](/source/Propagation_constant#Phase_constant), and complex [wavenumber](/source/Wavenumber), [complex refractive index](/source/Refractive_index) and [extinction coefficient](/source/Refractive_index#Dispersion_and_absorption), [complex dielectric constant](/source/Relative_permittivity), [electrical resistivity and conductivity](/source/Electrical_resistivity_and_conductivity). - Related measures, including [absorbance](/source/Absorbance) (also called "optical density") and [optical depth](/source/Optical_depth) (also called "optical thickness") All these quantities measure, at least to some extent, how well a medium absorbs radiation. Which among them practitioners use varies by field and technique, often due simply to the convention. ## Measuring absorption The [absorbance](/source/Absorbance) of an object quantifies how much of the incident light is absorbed by it (instead of being [reflected](/source/Reflection_(physics)) or [refracted](/source/Refraction)). This may be related to other properties of the object through the [Beer–Lambert law](/source/Beer%E2%80%93Lambert_law). Precise measurements of the absorbance at many wavelengths allow the identification of a substance via [absorption spectroscopy](/source/Absorption_spectroscopy), where a sample is illuminated from one side, and the intensity of the light that exits from the sample in every direction is measured. A few examples of absorption are [ultraviolet–visible spectroscopy](/source/Ultraviolet%E2%80%93visible_spectroscopy), [infrared spectroscopy](/source/Infrared_spectroscopy), and [X-ray absorption spectroscopy](/source/X-ray_absorption_spectroscopy). ## Applications Rough plot of Earth's atmospheric [transmittance](/source/Transmittance) (or opacity) to various wavelengths of electromagnetic radiation, including [visible light](/source/Visible_light) Understanding and measuring the absorption of electromagnetic radiation has a variety of applications. - In [radio propagation](/source/Radio_propagation), it is represented in [non-line-of-sight propagation](/source/Non-line-of-sight_propagation). For example, see [computation of radio wave attenuation in the atmosphere](/source/Computation_of_radiowave_attenuation_in_the_atmosphere) used in satellite link design. - In [meteorology](/source/Meteorology) and [climatology](/source/Climatology), global and local temperatures depend in part on the absorption of radiation by [atmospheric gases](/source/Atmospheric_gases) (such as in the [greenhouse effect](/source/Greenhouse_effect)) and land and ocean surfaces (see [albedo](/source/Albedo)). - In [medicine](/source/Medicine), [X-rays](/source/X-ray) are absorbed to different extents by different tissues ([bone](/source/Bone) in particular), which is the basis for [X-ray imaging](/source/Projectional_radiography). - In [chemistry](/source/Chemistry) and [materials science](/source/Materials_science), different materials and molecules absorb radiation to different extents at different frequencies, which allows for material identification. - In [optics](/source/Optics), sunglasses, colored filters, dyes, and other such materials are designed specifically with respect to which visible wavelengths they absorb, and in what proportions they are in. - In [biology](/source/Biology), photosynthetic organisms require that light of the appropriate wavelengths be absorbed within the active area of [chloroplasts](/source/Chloroplast), so that the [light](/source/Light) energy can be converted into [chemical energy](/source/Chemical_energy) within sugars and other molecules. - In [physics](/source/Physics), the D-region of Earth's [ionosphere](/source/Ionosphere) is known to significantly absorb radio signals that fall within the high-frequency electromagnetic spectrum. - In nuclear physics, absorption of nuclear radiations can be used for measuring the fluid levels, densitometry or thickness measurements.[2] In scientific literature is known a system of mirrors and lenses that with a laser "can enable any material to absorb all light from a wide range of angles."[3] ## See also - [Absorption spectroscopy](/source/Absorption_spectroscopy) - [Albedo](/source/Albedo) - [Attenuation](/source/Attenuation) - [Electromagnetic absorption by water](/source/Electromagnetic_absorption_by_water) - [Hydroxyl ion absorption](/source/Hydroxyl_ion_absorption) - [Optoelectronics](/source/Optoelectronics) - [Photoelectric effect](/source/Photoelectric_effect) - [Photosynthesis](/source/Photosynthesis) - [Physical crystallography before X-rays](/source/Physical_crystallography_before_X-rays#Absorption_and_pleochroism) - [Solar cell](/source/Solar_cell) - [Spectral line](/source/Spectral_line) - [Total absorption spectroscopy](/source/Total_absorption_spectroscopy) - [Ultraviolet-visible spectroscopy](/source/Ultraviolet-visible_spectroscopy) ## References 1. **[^](#cite_ref-1)** Baird, Christopher S. (September 2019). ["Absorption of electromagnetic radiation"](http://accessscience.com/content/Absorption-of-electromagnetic-radiation/001600). *AccessScience*. McGraw-Hill. [doi](/source/Doi_(identifier)):[10.1036/1097-8542.001600](https://doi.org/10.1036%2F1097-8542.001600). Retrieved 17 June 2023. 1. **[^](#cite_ref-2)** M. Falahati; et al. (2018). "Design, modelling and construction of a continuous nuclear gauge for measuring the fluid levels". *Journal of Instrumentation*. **13** (2): 02028. [Bibcode](/source/Bibcode_(identifier)):[2018JInst..13P2028F](https://ui.adsabs.harvard.edu/abs/2018JInst..13P2028F). [doi](/source/Doi_(identifier)):[10.1088/1748-0221/13/02/P02028](https://doi.org/10.1088%2F1748-0221%2F13%2F02%2FP02028). [S2CID](/source/S2CID_(identifier)) [125779702](https://api.semanticscholar.org/CorpusID:125779702). 1. **[^](#cite_ref-3)** ["Anti-laser enables near-perfect light absorption"](https://physicsworld.com/a/anti-laser-enables-near-perfect-light-absorption/). [Physics World](/source/Physics_World). August 31, 2022. - Thomas, Michael E. (January 2006). [*Optical Propagation in Linear Media: Atmospheric Gases and Particles, Solid-State Components, and Water*](https://books.google.com/books?id=EEodkQqPGs4C&q=absorption). Oxford University Press, USA. pp. 3... (Chapter 1, 2, 7). [Bibcode](/source/Bibcode_(identifier)):[2006oplm.book.....T](https://ui.adsabs.harvard.edu/abs/2006oplm.book.....T). [ISBN](/source/ISBN_(identifier)) [978-0-19-509161-8](https://en.wikipedia.org/wiki/Special:BookSources/978-0-19-509161-8). {{[cite book](https://en.wikipedia.org/wiki/Template:Cite_book)}}: |journal= ignored ([help](https://en.wikipedia.org/wiki/Help:CS1_errors#periodical_ignored)) - ProfHoff, Ken Mellendorf; Vince Calder (November 2010). ["Reflection and Absorption"](https://web.archive.org/web/20101121094449/http://www.newton.dep.anl.gov/askasci/phy00/phy00232.htm). *Physics Archive - Ask a scientist*. [Argonne National Laboratory](/source/Argonne_National_Laboratory). Archived from [the original](http://www.newton.dep.anl.gov/askasci/phy00/phy00232.htm) on 2010-11-21. Retrieved 2010-11-14. Authority control databases International GND National United States Other Yale LUX --- Adapted from the Wikipedia article [Absorption (electromagnetic radiation)](https://en.wikipedia.org/wiki/Absorption_(electromagnetic_radiation)) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Absorption_(electromagnetic_radiation)?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.