Absorption (electromagnetic radiation)

Quantifying absorption

• The absorption coefficient along with some closely related derived quantities
• The attenuation coefficient
• The molar attenuation coefficient, which is the absorption coefficient divided by molarity
• The mass attenuation coefficient, which is the absorption coefficient divided by density
• The absorption cross section and scattering cross-section, related closely to the absorption and attenuation coefficients, respectively
• "Extinction" in astronomy, which is equivalent to the attenuation coefficient
• Other measures of radiation absorption, including penetration depth and skin effect, propagation constant, attenuation constant, phase constant, and complex wavenumber, complex refractive index and extinction coefficient, complex dielectric constant, electrical resistivity and conductivity.
• Related measures, including absorbance and optical depth

Measuring absorption

Applications

• In radio propagation, it is represented in non-line-of-sight propagation. For example, see computation of radio wave attenuation in the atmosphere used in satellite link design.
• In meteorology and climatology, global and local temperatures depend in part on the absorption of radiation by atmospheric gases and land and ocean surfaces.
• In medicine, X-rays are absorbed to different extents by different tissues, which is the basis for X-ray imaging.
• In chemistry and materials science, different materials and molecules absorb radiation to different extents at different frequencies, which allows for material identification.
• In optics, sunglasses, colored filters, dyes, and other such materials are designed specifically with respect to which visible wavelengths they absorb, and in what proportions.
• In biology, photosynthetic organisms require that light of the appropriate wavelengths be absorbed within the active area of chloroplasts, so that the light energy can be converted into chemical energy within sugars and other molecules.
• In physics, the D-region of Earth's 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.