In this article, the New Scientist tells us about an amazing discovery about the control of light.
You don't often see claims of "unexpected and stunning new physical phenomena" in the abstract of a reputable scientific paper. But the latest report by photonics crystal pioneer John Joannopoulos and his group at MIT, soon to be published in Physical Review Letters, does not disappoint. The researchers document the ultimate control over light: a way to shift the frequency of light beams to any desired colour, with near 100 per cent efficiency.
Here is how it works.
When Joannopoulos and his colleagues Evan Reed and Marin Soljacic investigated what happens when shock waves pass through a device called a photonic crystal, they discovered a completely unexpected effect. Photonic crystals, which are made by sandwiching together layers of material that bend light in different ways, can be designed to reflect some frequencies while letting others through.
After 10,000 or so reflections, taking a total of around 0.1 nanoseconds, the light can shift dramatically in frequency- from red up to blue, for example, or from visible light down to infrared. By changing the way the crystal is built up, it is possible to control exactly which frequencies can go into the crystal and which come out. "We ought to be able to do things that have never been possible before," Joannopoulos told New Scientist.
What can we expect from this breakthrough?
Besides making devices such as light bulbs and solar cells more efficient, the method would also help to keep optical telecommunications networks moving. At the moment, many light frequencies are bounced down optical fibres simultaneously. If a particular frequency is being used to capacity, then optical switches could shift light beams to a frequency where there is still capacity to spare.
Another benefit of pushing the frequency of light downwards would be the ability to make terahertz radiation. Terahertz rays, in the range between microwaves and infrared, hold great promise for medical imaging, as they are easier to focus and less damaging than X-rays. But they're not yet widely used as they have been too difficult to produce.
Those of you interested by this subject can read a former column, "Is the Photonic Revolution Coming?"
Source: Charles Choi, New Scientist, May 21, 2003
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