all things NANO

Lasers from Quantum dots – Los Alamos team just solved the big problem June 14, 2007

This is really a important feat. For making a laser,you need to go through two steps – population inversion and stimulated emission. The inversion stage comes when the majority of the electrons in the material are in the excited state (conduction band). When this is the case, any incoming photon of the right energy “stimulates” the electron-hole pairs to recombine and emit two more photons.. This is stimulated emission, and leads to the photons getting amplified.

With Q-dots, the problem was that the pop inversion state lasts for a very very short time – less than 100 picoseconds. If you have to get emission within this time, you need some really fast lasers – which are really quite expensive.

These guys achived a breakthrough in this regard. I interviewed them and wrote an article for Optics magazine. You can find it here.

Quantum dots are really quite amazing substances. In a simple sense, they are like a container which holds electrons and holes in an incredibly small space. However, the confinement is not because they are like physical “containers”, but more because the bandgap values are specially tailored in a way that the charged particles cannot get out.