Attractive and repulsive light force

[junglebeast]

http://www.sciencedaily.com/releases/2009/07/090713131556.htm

I'm confused...photons have no charge and no mass. This article seems to say there is an attractive and repulsive force between photons, but that can't be electromagnetic and it can't be gravity..so what are they talking about?

[Born2bwire]

Well, there is a radiation pressure from light. Photons still have a momentum despite not having any mass and the transfer of the momentum will result in a force. But the article specifically states that these forces are not the product of radiation pressure so I think one would need to read the journal article to find out the specific mechanism.

[Andy Resnick]

I agree- the article is not exactly clear. It is claimed the force is a different effect from laser tweezers (which is casued by induced dipoles), but no information about their model is presented in that website.

[ZapperZ]

Here is the full abstract of this paper:

State-of-the-art advances in nanoscale optomechanics allow light to be guided in free-standing waveguides or resonators1,2. In closely spaced devices, the coupling between the guided lightwaves gives rise to an optical force known as the ‘optical bonding force’3–6. Indeed, attractive optical force has been observed in substrate coupled devices7. According to recent theoretical predictions3, the optical force should show bipolar behaviour depending on the relative phase between in-plane coupled lightwaves. So far, such an in-plane optical force has not been measured. Here, we experimentally demonstrate a bipolar optical force between planarly coupled nanophotonic waveguides. Both attractive and repulsive optical forces are obtained. The sign of the force can be switched reversibly by tuning the relative phase of the interacting lightwaves. This highly engineerable force of bipolar nature could be used as the operation principle for a new class of planar light force devices and circuits on a CMOS-compatible platform.

So it definitely appears that (i) this is a guided EM wave (ii) it is then similar to Casimir effect of bounded wave (iii) it is analogous to the "bonding" and "antibonding" state that we get in chemical bonds that depends on the phase of the wavefunction.

Reading the paper quickly, it definitely appears that this is a purely classical effect. It has nothing to do with a photon having attractive or repulsive force.

Zz.