two-photon absorption


two-photon absorption

[‚tü¦fō‚tän əb′sȯrp·shən] (physical chemistry) A relatively weak photon absorption and excitation process that occurs when a sufficiently intense light source, such as a laser beam, is used, making it possible for a molecule to absorb simultaneously two photons, each of approximately half the energy (twice the wavelength) normally required to reach an excited state. The probability of a molecule absorbing two photons simultaneously is proportional to the square of the intensity of the input beam.