[ZenGum]

An optical transistor that uses one laser beam to control another could form the heart of a future generation of ultrafast light-based computers, say Swiss researchers.

Conventional computers are based on transistors, which allow one electrode to control the current moving through the device and are combined to form logic gates and processors. The new component achieves the same thing, but for laser beams, not electric currents.
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To make their device, Vahid Sandoghdar and colleagues at the Swiss Federal Institute of Technology in Zurich, suspended tetradecane, a hydrocarbon dye, in an organic liquid. They then froze the suspension to -272 °C using liquid helium – creating a crystalline matrix in which individual dye molecules could be targeted with lasers.

When a finely tuned orange laser beam is trained on a dye molecule, it efficiently soaks up most of it up – leaving a much weaker "output" beam to continue beyond the dye.

But when the molecule is also targeted with a green laser beam, it starts to produce strong orange light of its own and so boosts the power of the orange output beam.

This effect is down to the hydrocarbon molecule absorbing the green light, only to lose the equivalent energy in the form of orange light.

"That light constructively interferes with the incoming orange beam and makes it brighter," says Sandoghar's colleague Jaesuk Hwang.

More here. And pics.