Spaser

SPASER is an acronym for "surface plasmon amplification by stimulated emission of radiation". The phenomenon was first described by Bergman and Stockman in 2003 [ [http://prola.aps.org/abstract/PRL/v90/i2/e027402 Surface Plasmon Amplification by Stimulated Emission of Radiation: Quantum Generation of Coherent Surface Plasmons in Nanosystems] , David J. Bergman and Mark I. Stockman, "Phys. Rev. Lett. 90, 027402 (2003)"]

The spaser is a proposed nanoscale source of optical fields that is being investigated in a number of leading laboratories around the world. If realized, spasers could find a wide range of applications, including nanoscale lithography, probing and microscopy.

A spaser is the nanoplasmonic counterpart of a laser [ [http://www.nature.com/nphoton/journal/v2/n6/full/nphoton.2008.85.html Spasers explained] , Mark I. Stockman, "Nature Photonics, 2, June, 327, (2008)"] , but it (ideally) does not emit photons. It is analogous to the conventional laser, but in a spaser photons are replaced by SPs and the resonant cavity is replaced by a nanoparticle, which supports the plasmonic modes. Similarly to a laser, the energy source for the spasing mechanism is an active (gain) medium that is excited externally. This excitation field may be optical and unrelated to the spaser’s operating frequency; for instance, a spaser can operate in the near-infrared but the excitation of the gain medium can be achieved using a UV pulse.

The reason that SPs in a spaser can work analogously to photons in a laser is because their relevant physical properties are the same. First, SPs are bosons: they are vector excitations and have spin 1, just as photons do. Second, SPs are electrically neutral excitations. And third, SPs are the most collective material oscillations known in nature, which implies they are the most harmonic (that is, they interact very weakly with one another). As such SPs can undergo stimulated emission, accumulating in a single mode in large numbers, which is the physical foundation of both the laser and the spaser.

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