Absorption (electromagnetic radiation)

Absorption is the transfer of electromagnetic energy into matter, reducing the radiation that passes through or is reflected from it. The absorbed energy can excite, heat, or otherwise change the material.

Photon: A photon is a quantum of electromagnetic radiation, carrying energy and momentum. Absorption transfers a photon's energy to matter.
Electromagnetic radiation: Electromagnetic radiation is energy carried through space or matter by coupled electric and magnetic fields. Absorption is one way electromagnetic radiation interacts with matter.
Absorption spectroscopy: Absorption spectroscopy identifies or measures substances by analyzing which wavelengths they absorb. It uses absorption bands as fingerprints of atoms and molecules.
Scattering: Scattering is the redirection of radiation by interactions with particles or variations in a material. Scattering redirects radiation rather than necessarily transferring its energy into matter.
Energy level: An energy level is a quantized value of energy available to a physical system. A photon can be absorbed when its energy matches an allowed transition between levels.
Transmittance: Transmittance is the fraction of incident radiation that passes through a material. A decrease in transmittance can signal absorption.
Atomic absorption spectroscopy: Atomic absorption spectroscopy measures elemental concentrations from light absorbed by free atoms. It applies element-specific absorption lines to quantitative chemical analysis.
Reflection: Reflection is the return of a wave from a boundary into the medium from which it came. Reflected radiation leaves a surface instead of being absorbed within it.
Electronic transition: An electronic transition is a change in an electron's quantum state, often caused by absorbing or emitting a photon. Visible and ultraviolet absorption commonly promotes electrons to higher-energy states.
Absorbance: Absorbance is the base-ten logarithm of the ratio of incident radiant power to transmitted radiant power. It expresses measured attenuation on a scale commonly used in spectroscopy.

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