“That light constructively interferes with the incoming orange beam and makes it brighter,” says Sandoghar’s colleague Jaesuk Hwang. This effect is down to the hydrocarbon molecule absorbing the green light, only to lose the equivalent energy in the form of orange light. 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.īut 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. They then froze the suspension to -272 ☌ using liquid helium – creating a crystalline matrix in which individual dye molecules could be targeted with lasers. 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. However, previous attempts to make optical transistors for such circuits only produced very weak effects.

Such “photonic” computing is desirable because components using optical fibres carrying light could be much faster than those using wires to carry electricity. This offers another possible route to light-based rather than electronic, computing.

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