If you ever watched Star Trek, I’m sure you’ve fantasized about one day being able to say, “Lock a tractor beam on that ship! Don’t let them escape!” It can’t be only me right?
Well, you know that there are definitely a couple of (thousand) physicists out there who want that sort of power. And the ones who have been working to that end have finally done it, albeit on a very small scale. And they called in tractor beams a la Star Trek.
The tractor beam in question uses a special type of beam called Bessel beams, which Chinese researchers last year theorized should be able to enable this function.
See Bessel beams send light in concentric circles around a single point, instead of directing light as a single beam. Since Bessel beams are not diffracted at their target point, this means that the light could technically reform on the other side of an object in its path. The Chinese research team figured out that if you direct the beam at a particle, the light reforming on the back end of the particle should be able to push the particle back towards the source.
David Ruffner and David Grier at New York University published a paper in Physical Review Letters that revealed they had in fact achieved this theoretical possibility. With 30 micrometre-sized silica spheres suspended in water.
The trick was that they had to use two beams, bent slightly using a lens so that they overlapped (coherently superimposed coaxial Bessel beams is the technical description of the resulting beams, for the physics nerds). The light alternating on and off from the end of the particle gave a strobe effect wherever you position the beam. The beam would provide the energy required to move the particle towards the light source, or away from the light source – the particle is essentially caught in an “optical trap”. The same method could then be used to send out a series of overlapped Bessel beams all around the object, which would allow transport through three-dimensions! Voila – tractor beam.
Ok so moving tiny little silica spheres through water may not seem super impressive right now but imagine the possibilities! While this model cannot be directly scaled up to move larger objects, since it would require way too much energy (and would likely destroy the objects it is trying to move in the process), it does show that it’s possible. Now all we need to do is figure out how to adapt the method to use less energy…and then we can start building the Enterprise.