[Elecraft] OT: Distinguishable angular momentum in radio photons?

[Jussi Eloranta]

On 05/04/2012 10:03 PM, Erik Basilier wrote:
> * The claim was not just that you can have two independent communications
> (as possible by means of circular polarization), but more than two.
> * The claim of multiple levels of angular momentum tells us that it is about
> OAM and not SAM. The abstract of the debunking research (thanks Sverre for
> posting) explicitly refers to OAM.
Indeed photons can posses orbital angular momentum which can only 
interact with materials that have fairly special anisotropic properties 
(which is the reason I was not even bringing it up earlier). In order to 
talk to the oam component, one should subject RF photons to propagate in 
such medium as well. While possible in theory (and shown in optics using 
an "obscure" version of a halve wave plate), it would be a real 
challenge to observe this for RF where such materials are not available 
(someone correct me if I am wrong, I mostly work with optics).

However, an interesting topic and well worth looking into! I wonder if 
photon orbital angular momentum would be conserved in a non-linear 
process where the difference and sum generation occurs (usually just the 
sum is used, for example in second harmonic generation; similar to RF 
heterodyning) and the difference component would lie in RF (OK, perhaps 
in GHz range in practice...; near baseband anyway ;-)? So the idea would 
be to start with optical photons (prepared with oam information) at 
close wavelengths and then convert to RF (RF wavelength = difference 
between the two optical photons; angular momentum must be conserved). 
Unfortunately, this would not work for detection that well because high 
intensities are needed for the non-linear process. I would expect that 
the first place where this would show up (if possible at all) for RF 
would be nuclear magnetic resonance (NMR) experiments where I could see 
that the extra source of angular momentum could find applications there.

I suspect that most people are getting bored already - so I will sign 
off...

Best,

Jussi Eloranta
AA6KJ