An Optically Pumped Nanocrystal Quantum Dot Laser

An optically pumped nanocrystal quantum dot laser has been demonstrated by a group at MIT. Lasers come in many sizes and can be made from a variety of resonant cavities and active laser materials.

Generally, increasing confinement enforces an increasing quantization in the energy of electrons. Therefore quantum dots, essentially zero-dimensional bits of material, will (once excited) re-emit light at nearly a single wavelength.

Quantum dots are therefore a good starting point for producing laser light. Some existing quantum dot lasers employ dots made epitaxially: the atoms in the dots are laid down meticulously using beams of atoms or molecules.

In the MIT laser the gain medium consists of nm-sized particles of CdSe coated with a layer of organic molecules and then immersed in a glassy film. The medium sits in a waveguide atop a grating. The fabrication advantage in this case derives from the fact that one uses simple solution processing rather than the more exacting technique of epitaxy usually needed for semiconductors.

Furthermore, the color of the output laser light can be varied by changing the size of the CdSe particles, the grating spacing, or the refractive index of the waveguide, giving great flexibility to the design and application of the laser. (Eisler et al., Applied Physics Letters, 17 June 2002; contact Moungi Bawendi, MIT, 617-253-9796, mgb@mit.edu.)