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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."
Just like my ex-girlfriend!
Dark Reflection
"Repulsive Force Discovered In Light"--well DUH. Anyone who's ever been in a strip club at closing time has witnessed this phenomenon.
Dear Slashdot: next time you want to mess with the site, add a rich-text editor for comments.
Actually, it's your spelling.
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.
Now emits 100% attractive light. That's twice as much as the next leading brand!
Here is a very good paper that might give you some insight.
http://www.opticsinfobase.org/DirectPDFAccess/7CB1DC52-BDB9-137E-C347E05AD6F7E2D4_84895.pdf?da=1&id=84895&seq=0&CFID=48237375&CFTOKEN=15548595
"Angular momentum of circularly polarized light in dielectric media"
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 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:
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.