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The Sciences

"Anti-Laser" Would Absorb the Light a Laser Shoots out

80beatsBy Joseph CalamiaAugust 4, 2010 8:33 PM

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Sure, a laser can shine finely-tuned light to do anything from scanning your barcodes to correcting your vision, but soon that precise hero may meet its match: Physicists have recently imagined a device that can absorb light of certain frequencies, an "anti-laser." Absorbing light may not seem all that impressive, since after all, anything that appears black works as an absorber. Your driveway, however, is not the anti-laser. A paper in the Physical Review Letters lays out the plans for this device which can absorb light wave clones (same frequency, phase, and polarization) that some lasers emit. The pickiness of this theoretical light absorber is part of what would make the device unique, just as an important part of what separates a laser from a flashlight is the precision of the light a laser emits.

Instead of amplifying light into coherent pulses, as a laser does, an antilaser absorbs light beams zapped into it. It can be “tuned” to work at specific wavelengths of light, allowing researchers to turn a dial and cause the device to start and then stop absorbing light. “By just tinkering with the phases of the beams, magically it turns ‘black’ in this narrow wavelength range,” says team member A. Douglas Stone, a physicist at Yale University. “It’s an amazing trick.” [Science News]

The Yale University team has gone through the numbers for such a choosy absorber, which works partly by switching the material that reflects light in a laser with material that instead absorbs it. The paper describes a theoretical device using silicon.

A paper-thin slice of silicon would normally absorb about 20 per cent of the incoming light, but the team showed that in this set-up it would cancel nearly all of the light at 945 nanometres, in the near infrared.... So far the effect exists only on paper, but team member Douglas Stone says "ongoing experiments are extremely promising, and I have total confidence it can be realised". [New Scientist]

Given the specificity of the light that this absorber requires it is unlikely, a Physics review says, to find future employment as part of a solar panel or stealth cloak (shielding a ship for example from radar). Instead, such a device could likely appear in pairs with lasers forming "optical switches" in circuits--and perhaps as the weapon of choice for science fiction foes. Related content: 80beats: Video: Navy’s New Laser Weapon Shoots Down Drones 80beats: NASA Satellites Use Lasers to Map the World’s Tallest Forests 80beats: Tattoo-Removing Lasers Also Remove Grime From Classic Works of Art 80beats: Found on the Moon: A Soviet Laser Reflector That Was Lost for 40 Years

Image: Wikimedia / Jeff Keyzer

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