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Supercontinuum tickle-spot offers analogue-to-digital leap

Boiling optical mega-waves mastered in analogy flurry

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Californian boffins say they have mastered the well-known phenomenon of freak waves - mathematically similar to the ship-swallowing monsters of the great southern ocean - occurring in supercontinuum light generators, by finding a magic optical "tickle-spot".

Daniel Solli, Claus Ropers, and Bahram Jalali of UCLA believe that their methods will make "supercontinuum" (SC) light much easier to handle. What, you didn't know about SC light? It's great stuff:

SC light is created by shooting laser pulses into crystals and optical fibers. Like the incandescent bulb in a lamp, it shines with a white light that spans an extremely broad spectrum. But unlike a bulb's soft diffuse glow, SC light maintains the brightness and directionality of a laser beam. This makes it suitable for a wide variety of applications -- a fact recognized by the 2005 Nobel Prize in Physics, awarded in part to scientists who used SC light to measure atomic transitions with extraordinary accuracy.

But it seems that SC light is tricky stuff to handle. In particular it's prone to unexpected wave pileups like those of the ocean, capable of producing the optical equivalent of a seven-storey wall of water able to crumple a supertanker like a paper cup. This makes SC light distinctly troublesome, and its great potential goes largely unexploited outside the labs of high-end physicists.

But Solli and his UCLA chums reckon they've cracked the snag, by developing a way of inducing the freak-wave SC light phenomenon under control. As they describe it, this is done by shooting a weak burst of light precisely into the "tickle-spot" of the SC generator. This causes the freak wave to happen at once, rather than much later and possibly much more severely as a result.

Thus the SC light still fluctuates, but hugely less than it did while subject to uncontrolled random freakouts. Solli likens the process to the boiling of water, which is a lot safer and easier if the water has some impurities in it for bubbles to form on.

"If you heat pure water, it can boil suddenly and explosively," he says. "But normal water has nucleation sites for bubble formation that - like our seed waves stimulate the supercontinuum - help the water boil smoothly with less heat."

According to the boffins, SC light, tamed by the use of their tickle-spot technology, could be handy stuff indeed. It could result in "better clocks, faster cameras, and more powerful radar and communications technologies". In particular, they think that a major SC-light building block for new radar and comms would be a "new optical analog-to-digital converters 1,000 times faster than current electronic versions", which is now on the cards.

The UCLA brainboxes will present their research at a conference in San Diego later this month. ®

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