Spaser on a wire: tiniest lasers
The laser is a very special light source: the spatial, temporal, and frequency aspects of laser light can be exquisitely controlled. This control has enabled much of modern life, and it has had a major impact on research itself. But even the smallest laser is rather large. And many of the things we like to do with light, like imaging, are limited by the fact that normal optical elements can only focus light to a spot with a diameter that is something like the wavelength of light.
To compensate for this shortcoming, researchers have turned to the world of surface plasmon polaritons. The nice thing about plasmons is that they involve an interaction between electrons in a metal and a light field that leads to the wavelength becoming much shorter. The result is that plasmon optics are much smaller and can focus light to much smaller spot sizes.
The dirty little secret of plasmons is that they decay away very quickly, making them tough to work with. To overcome this, researchers are working on plasmonic laser sources, called spasers.
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