What does it mean to change the polarization of a laser beam

[mrspock]

http://www.iflscience.com/physics/p...r-tractor-beam-functional-over-long-distances

In this article, they said they could control the particle's direction by changing the laser's polarization.

Could someone explain this to me? I have to do a presentation on it next week.

 

[e.bar.goum]

Maybe it would help if you could ask some more specific questions. If you're doing a presentation on it next week, you must have done some research already. Have you read the paper? What questions do you have from reading the paper?

 

[mrspock]

I read the article and understand most of it. It's just how they said that they can change the direction the particle moves by changing the laser's polarization. I don't know what polarization is, what does it mean to change the polarization of a laser beam?

 

[e.bar.goum]

I really rather doubt you understand the paper if you don't know what polarization is. Polarization is mentioned everywhere in the paper, from the abstract on down. It's rather crucial to the operation of the experiment.

Electromagnetic waves oscillating in space have an orientation - this is the polarization of the wave. Since the magnetic and electric parts are normal to each other, we normally define polarization as the orientation of the electric field. If the electric field is always in a single direction, we say that the light is linearly polarized. If you rotate the electric field around, the light is circularly polarized, and so on. Shown schematically here: http://upload.wikimedia.org/wikiped...Polarizer_Creating.Left.Handed.Helix.View.svg

By cleverly constructing the polarization of the laser beam to be radially or azimuthally polarized, the experimenters have made a stable tractor beam. See fig. 2 of the paper.

This is quite good: http://en.wikipedia.org/wiki/Polarization_(waves)
As is this: http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/polarcon.html