Inspectroscopy, the Dicke effect, also known as Dicke narrowing or sometimes collisional narrowing, named after Robert H. Dicke, refers to narrowing of the Doppler broadening of a spectral line due to collisions the emitting species (usually an atom or a molecule) experiences with other particles.[1][2]
When the mean free path of an atom is much smaller than the wavelength of the radiative transition, the atom changes velocity and direction many times during the emissionorabsorption of a photon. This causes an averaging over different Doppler states and results in an atomic linewidth that is narrower than the Doppler width.
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