An overview of absorption ofelectromagnetic radiation. This example shows the general principle usingvisible light as a specific example. A whitelight source—emitting light of multiplewavelengths—is focused on a sample (the pairs ofcomplementary colors are indicated by the yellow dotted lines). Upon striking the sample,photons that match theenergy gap of themolecules present (green light in this example) areabsorbed, 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 theattenuation of light for various wavelengths, anabsorption spectrum can be obtained.
A notable effect of the absorption of electromagnetic radiation isattenuation of the radiation; attenuation is the gradual reduction of theintensity oflight waves as theypropagate through a medium.
Although the absorption of waves does not usually depend on their intensity (linear absorption), in certain conditions (optics) the medium's transparency changes by a factor that varies as a function of wave intensity, andsaturable absorption (or nonlinear absorption) occurs.
Related measures, includingabsorbance (also called "optical density") andoptical 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.
Theabsorbance of an object quantifies how much of the incident light is absorbed by it (instead of beingreflected orrefracted). This may be related to other properties of the object through theBeer–Lambert law.
Inmedicine,X-rays are absorbed to different extents by different tissues (bone in particular), which is the basis forX-ray imaging.
Inchemistry andmaterials science, different materials and molecules absorb radiation to different extents at different frequencies, which allows for material identification.
Inoptics, 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.
Inbiology, photosynthetic organisms require that light of the appropriate wavelengths be absorbed within the active area ofchloroplasts, so that thelight energy can be converted intochemical energy within sugars and other molecules.
Inphysics, the D-region of Earth'sionosphere 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]
