Superradiance is a phenomenon of collective emission of an ensemble of excited atoms or ions, first considered by Dicke . It is similar to superfluorescence, but it starts with the coherent excitation of the ensemble, usually with an optical pulse. This coherence (i.e. a well-defined phase relationship between the excitation amplitudes of lower and upper electronic states) leads to a macroscopic dipole moment. The maximum intensity of the emitted light scales with the square of the number of atoms, because each atom contributes a certain amount to the emission amplitude, and the intensity is proportional to the square of the amplitude. This demonstrates that the emission of light in a medium is in certain cases not just an intrinsic property of the atoms or molecules of which the medium consists, but rather can be strongly enhanced by a collective behavior of such emitters.
The term superradiance can be understood by considering that it can also lead to very high values of radiance.
As the number of photons rises in a kind of chain reaction, Dicke later (in a patent application) described the phenomenon of superradiance as an optical bomb.
There is the related effect of superabsorption , which can be seen as time-reversed superradiance .
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