Re: What exactly is twisted light ?

  Hi John,

 It is very interesting question.. I will try to answer. I hope, I can 
help you with this answer.. You can find an answer your question about 
Orbital Angular Momentum of light in the following link..
 http://www.aip.org/png/2005/229.htm

On the other hand difference between polarized light and it is clear in 
this link. In ordinary light beam(vertically or circularly polarized 
light), the electric fields at every point of the cross section are in the 
same phase. But in a beam with orbital angular momentum, different points 
on the cross section are in different phases.

You say:" I saw an article that someone made dust particles move in a 
circle when illuminated by a beam of twisted light. Is there a relatively 
inexpensive way of doing this as a class demonstration?"

If you have a laser, it is simple.. 



    laser------ objective ---- Specimen plane..

 You can trap dust particles by this setup(above).. 

 Good Lucks..


  Best wishes