Now they have something that works like a flatbed document scanner, with a scanning head containing either six or 12 light-emitting diodes, each emitting light of a specific wavelength between 350 nanometres (ultraviolet) and 800 nanometres (infra-red).

ECONOMIST: Monitor

By tuning the quantum cascade laser and measuring how much of the infra-red radiation is absorbed on its way to a detector, hazardous gases in between can be identified.

ECONOMIST: Lasers

Infra-red communication suffers the same problems, but has the additional limitation of requiring a direct line of sight between objects as anyone who has tried to operate a television remote control with someone else standing between him and the television will know.

ECONOMIST: The human body as a computer bus