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Party Trick #185: Turning A Laser Into A Tractor Beam

By 03.02.11

Ahhh yeah ya’ll, I hope everybody brought along an extra change of clothes today -things are about to get sweaty and sexy- because we’re gonna’ be discussing lasers, folks, specifically how one might turn a laser into a tractor beam. Don’t say I didn’t warn you, but the temperature is about to go up. I’m taking off my socks now, just so everyone is aware.

Alright, so for a while now it’s been a scientific fact that photons have a momentum that they can pass onto anything they collide with. In using that momentum, when the photons run into something and that transfer of force occurs, the photons demonstrate a pushing effect. New to this concept is the idea that photons could then also perform a pulling result if needed. At least this is the argument that Jun Chen and his pals from Fudan University in China are trying to prove right now.

Oh right, about the lasers and tractor beams and robots and stuff…

Chen and his team claim that by using a forward propagating laser beam they’ve somehow worked out the details of how to create a backwards pulling force from it -so they claim.

Chen and buddies say this is possible when the system meets two conditions. First, it works only for beams in which the momentum in the direction of propagation is small, as is the case for beams that merely glance off an object. Second, the photons must simultaneously excite several multipoles within the particle, which scatter the beam.

If the scattering angle is just right, the total momentum in the direction of propagation can be negative, meaning the particle is pulled back towards the source and the light becomes a tractor beam. [TechnologyReview]

At this point, the concept is only a theory paper from Chen and colleagues, so until they can prove the demonstration, they’ll have to reserve from making it rain at the strip club. The article is published by MIT, who start to nerd out and explore the potential uses for tractor beams in the near future; getting all romantic talking about how NASA could potentially use the beams to clean up space junk. Me, I was thinking a little more locally, like how to get that TV remote into my palm without getting up from the couch, for example.


TAGSCHINAFudan UniversityJun ChenLASERSNerdstractor beam

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