Subject: What exactly is twisted light ?

Please define the orbital angular momentum of light(i.e. twisted light) and 
how it differs from the regular angular momentum of light. And how does it 
differ from circularly polarized light? Please explain in a way I can get a 
mental image of what these things are. I've read that it is a relatively 
recently discovered fundamental property of light (about ten years ago or so) 
and it's very interesting but I can't get a mental picture of it and how it 
differs from the other angular momentum of light. 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? Thanks a lot!

Re: What exactly is twisted light ?