A Superradiant Amplifier

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Science  15 Nov 2013:
Vol. 342, Issue 6160, pp. 779
DOI: 10.1126/science.342.6160.779-b

The usual notion of laser operation involves populating an excited state of a gain medium so that there are more atoms in the excited state than there are in the ground state. This population inversion can then be stimulated to emit many photons coherently with the same wavelength. The spontaneous emission of photons from atoms is a common occurrence, but the conditions for lasing cannot always be met. Six decades ago, it was shown theoretically that an ensemble of spontaneously emitting atoms could, under the right conditions, behave collectively and emit in unison, thereby giving rise to superradiant emission. In this scenario, population inversion is not necessary. Svidzinsky et al. show that a driving field of infrared light illuminating the superradiant ensemble can result in the amplified emission of coherent light but at much higher frequencies. If experimentally realized, their proposed mechanism could provide a route for the generation of coherent radiation in the UV or even x-ray range of the electromagnetic spectrum.

Phys. Rev. X 3, 041001 (2013).

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