Definition of absorption line

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Photonics Dictionary

absorption line: An absorption line is a dark line in a spectrum that occurs when a specific wavelength of light is absorbed by atoms or molecules in a medium (such as a gas or a solid) as light passes through it. This absorption happens because the energy of the light at that specific wavelength matches the energy difference between two quantized states of the atoms or molecules, causing them to transition from a lower to a higher energy state.

Formation: Absorption lines form when photons of a specific energy (or wavelength) are absorbed by electrons in an atom or molecule, causing the electrons to move to higher energy levels. This results in a decrease in the intensity of light at that specific wavelength, creating a dark line in the observed spectrum.

Spectroscopy: In spectroscopy, absorption lines are used to identify the presence of specific elements or compounds within a sample. Each element or compound has a unique set of absorption lines, serving as a fingerprint for its identification.

Astronomy: Absorption lines are crucial in astronomy for determining the composition, temperature, density, and motion of celestial objects. By studying the absorption lines in the spectra of stars and galaxies, astronomers can infer the presence of different elements and molecules in those objects and their intervening media.

Applications: Absorption lines are used in various scientific fields, including chemistry, physics, and environmental science, to analyze the composition and properties of substances. Techniques such as atomic absorption spectroscopy (AAS) and molecular absorption spectroscopy rely on the detection of absorption lines.

Examples: Common examples of absorption lines include the Fraunhofer lines in the solar spectrum, which are caused by the absorption of specific wavelengths by elements in the Sun's atmosphere, and the lines observed in the spectra of distant stars and galaxies due to the intervening interstellar medium.

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