Re: POLARIZATION

[brian whatcott <inet@intellisys.net>]

At 15:39 6/15/98 -0700,Leigh wrote:

> Please point out for the slower of those among us: what are you
> arguing, and where is the argument? I surely don't see it. What
> is the proposition? What are the assumptions?

It will help if I here reproduce the question which I attempt to answer:

------------------------------------------------------------
At 12:13 6/13/98 -0700, [James McLean] wrote:
....
> If linear polarization can be described as a superposition of circular
> polarization, and vice versa, how can one be more 'basic' than the other?
>
> --James McLean

" Here's a weak, quantum argument:

" A linear wave has twice the amplitude of its two component helical waves.
" A helical wave has the same amplitude as its component linear waves.
" In the limit, smaller helical waves are permitted than linear waves. QED
------------------------------------------------------------


This is a 'reductio' argument for the least possible magnitude of two
 components of an electromagnetic wave which can yet synthesize a wave 
of a combined type. 

 I say here that if two helical waves can have smaller amplitude than 
the least amplitude of a linearly polarized wave, then ipso facto the
 helical waves may be said to be more basic or fundamental than linearly
polarized waves.
One concludes that some equivalent of circular polarization exists at the
quantum level, and one supposes this to be a 'spin' property.

 I see that not only is this 'weak' but difficult to follow as well?

> [Leigh]
> I don't know what photopolarization is, either. Should I?

I would have thought that a radio amateur (as Leigh has sometimes 
described himself) might also remark that the polarization of an 
electric dipole at radio frequencies is to be thought of as a 
statistical effect; for the quantum energy available at these low 
frequencies implies that very many photons would be associated with 
even the few watts emitted as plane polarized waves by say a cell-phone.

  An electrochemist, by contrast, might tend to associate polarization 
with polarography than polarimetry; he would be alerted by the "photo-"
 prefix, I had hoped?
> *A* photon picture is entirely adequate to model polarization
> phenomena. *No* model explains all electrodynamic phenomena
> except in an *ad hoc* manner.
>
> Leigh
Leigh seems to have let passed unnoticed my recent assertion that his 
"adequate photon picture" appears to have lead him into error in 
connection with the putative lack of angular momentum or spin of a 
single photon, "transmitted or not" as he recently asserted.
 I will take this opportunity to replay this interesting thread
as a rebuttal:

-------------------------------------------------------------------
At 17:35 6/11/98 -0700, Leigh answered this question as follows:

> > So can one account for the phenomenon (of polarization) in terms of the
> > interactions of spinning photons with the polarizer?
[Leigh]
> If one considers the interaction of a circularly polarized
> photon with a (dissipative) linear polarizer, then its
> angular momentum is absorbed by the polarizer whether it
> is transmitted or not.

[Me - bw] 
" This statement appears to be completely in error, if by circular 
" polarization of a single photon one is referring to its spin.
" A photon has spin or it is not a photon.
" I expect Leigh had some other meaning in mind.
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I attempted in my introductory text to make clearer the "quantum argument" 
which I employed as a basis for the claim that helical polarization is 
a more fundamental property than linear polarization.
This represented my answer to James McLean's question: which polarization 
type is more basic.

I suppose that helical polarization is likely to be a manifestation of 
the 'spin' value associated with a photon because it is not usually held 
that an individual photon may exhibit properties such as polarization,
considered as a seperate parameter.

Having attempted to expand my position, I can ask if now Leigh would 
favor us in turn with his explanation for the surprising statement that 
a photon can lose its angular momentum and survive?

Sincerely

Brian Whatcott     Altus OK