Repulsive Force Discovered In Light

Aurispector writes in with news that the Yale team that recently discovered an attractive force between two light beams in waveguides has now found a corresponding repulsive force. "'This completes the picture,' [team lead Hong] Tang said. 'We've shown that this is indeed a bipolar light force with both an attractive and repulsive component.' The attractive and repulsive light forces Tang's team discovered are separate from the force created by light's radiation pressure, which pushes against an object as light shines on it. Instead, they push out or pull in sideways from the direction the light travels. Previously, the engineers used the attractive force they discovered to move components on the silicon chip in one direction, such as pulling on a nanoscale switch to open it, but were unable to push it in the opposite direction. Using both forces means they can now have complete control and can manipulate components in both directions. 'We've demonstrated that these are tunable forces we can engineer,' Tang said."

Angular momentum

[TiberSeptm]

Huh, I had always wondered how to resolve conservation of light's angular momentum during destructive interference of collinear laser pulses consisting of phtons of the same "handedness." I wonder if this can be used to explain that.

Re:Angular momentum

[TiberSeptm]

Sorry about the double post, but I was reading an old paper on the subject. Light has a lower angular momentum inside an dialectric than in air or vaccum. This means that it imparts a force upon entering a dialectric and upon exiting a dialectric. If it is combined out of phase within the dialectic, then destructive interference will mean that the entering and exiting force imparted by the light beams will be out of balance (as the intensity of the exiting beam will be lower without any radiation-pressure type interactions being required) and there will be a net repulsive force. I wonder if this is the same thing as what they are seeing in the article.

Re:Psssssssshhhhhhh!!!!!!

[TiberSeptm]

I always assumed it was a misnomer and they were just very skillfully manipulated plasma devices. We already have the technology to create "plasma windows" that can hold back atmosphere against a vacuum and plasma torches than can cut through cowboynelium. Why not bridges and swords of the highly charged fun-stuff?

Nice. But.

[terbo]

While discovering new properties of old phenomena is interesting,
does anyone ever question the 'bravado' of the wording of such
discoveries?

Does it inhibit later discoveries, in creating artificial limitations
through language and subsequently expectation?

Maybe with metamaterials.

[TiberSeptm]

Possibly, but this looks like the effect of light beams interacting inside of a target dialectric combined with the differences in light's angular momentum at the different speeds of c inside and outside the target. Aside from also cooking whatever you wanted to tractor, you might be able to accomplish this with very powerful laser pulses and "cloaking" metamaterials. Since the metamaterials bend the relevent light frequencey around a target you may be able to exert the force on the material, use a vastly powerful laser pulse, and not cook the target. This could impart enough force to be useful and could be used to maintain a cloud of such objects over vast distances using a web of laser pulses pushing and pulling the disparate objects into a desired position. Kind of a neat idea and a good intuitive leap to suggest tractor beams

http://www.msnbc.msn.com/id/12961080/ [msn.com]

So Earth Finally Discovers It!

[TheWanderingHermit]

So Earth finally discovers the repulsive force from the ninth light ray that they've known about on the dying planet of Barsoom for millennia. Does that mean that soon we can have navies of huge floating ships like the Kingdom of Helium does? Or that soon we'll be able to see the two colors they know about on Barsoom that we've never seen on Earth?

Observation of distant objects....

[zekt]

As I understand it, current thinking is that light bends because of gravity, and this is how distant planets and other distant objects are found.

Could it be that it is, instead, is just light being pulled or pushed against something that is being observed, rather than an observation of the gravity that the body has?
The next effect is the same I guess.

Re:Psssssssshhhhhhh!!!!!!

[nessus42]

They were successful in creating an effective lightsaber in that it had a definite end point and would cut through anything, but when they attempted to cross swords, they just passed through one another... and then one of the people cut through the other one with the lightsaber he had. You can probably find it on youtube or on theforce.net somewhere...

Indeed you can find it on YouTube. Here it is:

          http://www.youtube.com/watch?v=dsZNiCSCLXw [youtube.com]

|>ouglas

How does this fit into the Standard Model? Nicely.

[MillionthMonkey]

When light shines through a diffraction grating and spreads out into beams going right and left, we don't need to talk about some strange new "force" that pushed the rightward beams to the right and the leftward beams to the left, since it's still a manifestation of electromagnetism. But specifically quantum electrodynamics, not classical electromagnetism which isn't good at handling this stuff.

In this case, the fundamental reality is, of course, that each photon splits up at the grating and its wave function takes all paths- interfering with itself everywhere in space. When the photon is discovered hitting a screen, it will strike in a place that reveals the least amount of information about the path it actually took, and there will be many such places, called "interference maxima". (It probably won't land in a place that makes it obvious how it got there- such places are interference minima.)

The Casimir force [wikipedia.org] is another "force" like this. Underneath it's still quantum electrodynamics.

If you find this stuff interesting you should read Feynman's QED... basically Quantum Electrodynamics For Dummies. What you'll find is interesting:

• Light can go faster than light or slower than light- but only briefly
• Light really doesn't care about surfaces between air and water and glass or whatever
• Light doesn't really go in straight lines, that's just sort of how things turn out

These guys are sending beams of IR photons down a channel that is 220nm x 220nm, smaller than their wavelength. So transverse wave motion isn't a consideration at all... the light can barely fit in there and its wavefunction inside has no longitudinal component. I think it can be totally described with two scalar functions along the waveguide. The photons have apparently been through a beamsplitter or something and are being recombined out of phase. It's too bad the article doesn't provide any further details on how the photons were polarized (circular, linear, what?) or how the quantum interference between the two photon states results in transverse forces on the waveguide.

Re:Psssssssshhhhhhh!!!!!!

[Anonymous Coward]

You *have* seen this, haven't you?

http://www.wired.com/dangerroom/2009/07/darpas-handheld-nuclear-fusion-reactor/