If I understand your question..

You can prepare waves in such a way that forces them into this spiraled waveform state. This can be done in a cavity (in the case of lasers) as there are solutions of the wave equation that give rise to OAM; or this can be done by using diffractive optics, like a hologram, that somewhat force the wave into this state. It is this case that you can think of a torque being exerted onto the waves.

Waves too, can exert torque on small particles (micron sized polystyrene spheres for instance). Light with spin or orbital angular momentum can be used to make these small object rotate!

> Light with spin or orbital angular momentum can be used to make these small object rotate!

Thank you, that was exactly the effect I was looking for. Any links handy? Fascinating stuff, this from an old microwave-digital guy.

Sure! Here's a research group in Glasgow that has a great site: http://www.physics.gla.ac.uk/Optics/play/photonOAM/

And here is the lab where I did my undergrad research (Colgate Univ.): http://departments.colgate.edu/physics/research/optics/oamgp...

happy to offer up my phd thesis as well: http://shel.tv/henry_thesis

If you ever find yourself in Santa Monica, the beer is on me.