Physicists Build World's First Antilaser

One laser beam can be used to extinguish another. This is not a potential defense to laser weapons. It is not entirely clear what its ultimate use will be. The front runner is that it will be user with increase the speed of computing or medical imaging. The technology, even when viewed as a concept, is still young. It may yet be found to have important applications in other fields as well.

http://www.wired.com/wiredscience/2011/02/real-live-antilaser

"Less than a year after it was first suggested, the world’s first antilaser is here. A team of physicists have built a contraption that, instead of flashing bright beams, utterly extinguishes specific wavelengths of light.

Conventional lasers create intense beams of light by stimulating atoms to spit out a coherent beam of light in which all the light waves march in lockstep. The crests of one wave match the crests of all the others, and troughs match up with troughs.

The antilaser does the reverse: Two perfect beams of laser light go in, and are completely absorbed.

“There will be nothing coming out again,” said experimental physicist Hui Cao of Yale University, whose research group built the new device.
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The device can only absorb one wavelength of light at a time, but that wavelength can be adjusted by changing the thickness of the wafer.

Surprisingly, the antilaser switched from absorbent to reflective when the researchers changed the way the waves met in the wafer. Under certain conditions, the silicon crystal actually helped light escape.

“That is a little surprising,” Cao said. “We can turn it on and off.”

Theoretically, 99.999 percent of the light can be extinguished. Because of the physical limitations of the laser and the silicon wafer, the antilaser only absorbed 99.4 percent of the light."