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Re: POLARIZATION

Hmmm. I can see that I need to speak more directly to David's discomfort with
the description I gave which mentioned optically active materials.

1) It is not quite appropriate (in my view) to allude to particals
(or even particles) when one is discussing a facet of electromagnetic
radiation which is evidently wave-like.

2) The quotation given by David as emanating from Voss is clearly wrong.
I hasten to add that its 'wrongness' may issue only from an incompleteness
of the quotation.

To justify this bald assertion, I repeat that it is a fundamental
requirement of any helically polarized electromagnetic radiation (which is
often called circularly polarized) that it must be analyzable into two
orthogonally polarized components which differ in phase by a quarter wave
at the frequency of interest.

Let me make this quite clear: the superposition of two waves of one
quarter wave phase difference but of the same polarization leads only to a
non-rotating wave of intermediate phase. This is David's principal error,
in my view.

3) Optical activity occurs in solids and in liquids and gases.
Some materials maintain their stereoactivity in all these states; others do
not.

David appears to be fixated on the solid crystal form. The definition I
quoted for stereoactive materials refers specifically to those deriving
their activity at the molecular level. It is requoted below in the sentence
beginning
"In stereo-chemistry...."

Perhaps I should mention that it issues from the article written by Joseph
B Lambert (Northwestern U) for the third ed. of Encyclopedia of Chemistry,
Hampel & Hawley, Van Nostrand-Reinhold.

4) Whether one particle is sequentially more rotated than another, I
suggest owes more to a person's particular conceptual model rather than to
experimental results.
I am more than willing to see documented references to such photon particle
orientations however.

Finally, I should mention, once again, that I feel that I am arguing from
an unfairly advantaged position: I know quite well what happens when one
transmits from a wire helix antenna and I am inclined to consider that such
behavior persists up to optical frequencies. I know just as well, that two
orthogonally oriented dipoles at an odd multiple of a quarter wave will
replicate this behavior (so long as the helix direction is observed).

In characterizing both David and his authority, Voss as wrong, I hope I am
making my postion clear in this area now.

Brian Whatcott



At 15:14 6/10/98 EDT, you wrote:
Perhaps in our informal e-mail descriptions we just aren't communicating
very clearly. My problem was not with the handedness or corkscrew nature
of the circularly polarized light but with the idea that light became
polarized
like this by following a corkscrew path through the crystal. The corkscrew
nature of polarized light is simply an artifact of vector addition. A
"partical" of light that emerges from a crystal with a certain polarization
does not rotate once it leaves the crystal. However, the next particle to
leave will be slightly rotated from the first, thus creating a corkscrew
pattern in space. As the circularly polarized light advances through an
isotropic medium the corkscrew does not turn, it simply advances.
While the circularly polarized light has a handedness optically active
crystals need not have a handedness in their crystal structure.
One can produce other handed circularly polarized light simply by changing
the angle of incidence of the linearly polarized light incident on the 1/4
wave plate. It is not necessary to change the 1/4 wave plate. Circularly
polarized light is simply the result of interference caused by phase
differences.
on Fri, 05 Jun 1998 16:18:36 -0500 brian whatcott said:
David seemingly had some difficulty with my classification of 'left hand'
and right hand' polarizations of EM waves.
Nevertheless, that's how it is!

And at below VHF on up through light frequencies, it is quite rational to
describe a circular ( properly helical) polarization as a quarter wave
displacement of orthogonal components, as he does.

But perhaps David has forgotten that the sense of the quarter wave
displacement (advanced or retarded) determines the handedness of such
electromagnetic waves.

Brian Whatcott Altus OK


At 15:18 6/4/98 EDT, David wrote:
You are making circular polarization much more complicated than it
really is.
Let me quote from An Introduction to the Methods of optical
Crystallography by
Donald Bloss. "If the path difference between the two waves emergent
from a
crystal is lambda/4 (or any odd multiple of lamda/4) their vibrations
interfere
where they coincide in space and time, to produce resultant vibration
vectors
of constant lengths but variable azimuths..." There is no need to invoke
handedness or corkscrew paths. ...

On Fri, 29 May 1998 10:09:12 -0500 brian whatcott said:
It is not difficult to configure an array of dipoles, yagi style, so that
the polarization angle is changed. Just a matter of geometry of
conductors.

In stereo chemistry, stereoactive materials are classified as
configurational, geometric and conformational isomers which involve either
chirality (handedness, or non superimposability of a mirror-image) or
rotation of some part of a molecule round a double or single bond.
...
Brian Whatcott Altus OK