Re: light slows down in glass

["Bob Sciamanda" <trebor@velocity.net>]

-----Original Message-----
From: LUDWIK KOWALSKI <KOWALSKIL@alpha.montclair.edu>
To: phys-L@atlantis.uwf.edu <phys-L@atlantis.uwf.edu>
Date: Saturday, February 07, 1998 1:19 AM
Subject: Re: light slows down in glass


> > Date: Fri, 06 Feb 1998 22:30:16 -0500
> > From: Bob Sciamanda <trebor@velocity.net>
> > Subject: Re: Light slows down in glass?
>
> > .... Introducing matter into this ALREADY EXISTING field will produce
> > secondary radiation sources out of each mobile charge IMMEDIATELY.
>
> You are referring to electrons in a dielectric material; nearly all of
> them are bound to molecules. They are classical oscillators DRIVEN by
> the EM wave. How is n defined in theoretical electromagnetism? Can you
> define it without accepting the fact that the phase velocity is changed
> in the medium? Is this not what we are trying to explain?

For a dielectric, change "each mobile charge" to read "polarized matter" for
a more explicit description of the model.
n is defined in terms of the phase velocity of the resultant field.  This is
a result of the calculation, not a given input.  (The presence of polarized
matter is the input.)

> The concept of "DRIVEN mobile charges" does not correspond to the
> "absorption and reemission" model called Huygens principle. Do you
> agree that the "naive Huygens principle" can not be used to answer
> the main question of this thread? You are trying to provide an
> alternative model. Am I interpreting you correctly?
>                                                     Ludwik Kowalski

In order to use Huygens principle alone to model a change of medium, you
must take the new value of n as a given input.  The "scattering" model takes
only the presence of polarized matter ("scattering centers") as the input
and outputs the index n as a description of the phase velocity of the
resultant radiation field.

Huygens' principle is a very useful calculational tool (with limitations)
but  limps very badly (IMHO) as a "physical, conceptual" mechanism (even -
no, especially - as traditionally applied to diffraction by material
obstacles in otherwise free space).

The Maxwellian scattering model which I am describing is calculationally
parallel to Feynman's "sum of probability amplitudes" model and gives
identical results.  As R.P. says in QED,  the photon notion only needs to be
injected to make palatable the quantized nature of the detection process;
otherwise Maxwellian optics is just as useful a model.

> > The original field still exists everywhere, and there will be a
> > transient period during which the secondary and original waves
> > superimpose into a steady state wave pattern whose PHASE VELOCITY
> > is c/n (given a transparent material).  The "extinction theorem" of
> > Omnes (1915) examined this model in detail (Cf Born & Wolf's Optics
book).

-Bob

Bob Sciamanda   sciamanda@edinboro.edu
Dept of Physics   trebor@velocity.net
Edinboro Univ of PA  http://www.edinboro.edu/~sciamanda/home.html
Edinboro, PA   (814)838-7185


"Although this may seem a paradox, all exact science is dominated by the
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