Artificial atoms amplify light

A UK-Swiss team describes how it generated laser light without the need for a population inversion in the current issue of Nature Materials.

Physicists have found a new way to amplify light that could make lasers more efficient. Chris Phillips at Imperial College in London and colleagues at the University of Neuchâtel in Switzerland made the breakthrough using specially patterned nanocrystals that behave as artificial atoms.

Because the separation between energy levels in their crystals can be controlled, laser light can be produced without the need for a population inversion. The technique could also find applications in optical data storage and even allow materials to become completely transparent (Nature Materials 5 175).

The active medium in a laser is usually a gas or a crystal in which the atoms have been excited or "pumped" so that more electrons exist in the upper of two energy levels. Once such a population inversion has been achieved, a beam of light passing through the medium can stimulate electrons to fall into the lower energy level and emit a photon of the same wavelength. The emitted photons then go on to de-excite further atoms, amplifying the original beam.More at optics.org