Seeing infra-red

THE semiconductor laser is best known for its contribution to the living room. Without a laser small enough to fit on a chip, you would not be able to listen to music on your compact-disc player. In principle, similar lasers might be used for a different set of applications—notably to detect low concentrations of chemicals. But for this purpose they would have to shine not in the red (like the laser in a CD player) but in the infra-red. And making semiconductor lasers of this sort is trickier. A group of scientists headed by Federico Capasso at Bell Laboratories (part of Lucent Technologies) in New Jersey has therefore been working on getting infra-red light from an alternative device. It is called a quantum cascade laser.