How To Turn A Laser Into A Tractor Beam
Physicists work out how to generate a backward pulling force from a forward propagating beam
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.
This is a theory paper so there's one piece of the puzzle left to fit. All they have to do now is demonstrate that their tractor beam works.
Via Technology Review
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