From: crb7q@kelvin.seas.Virginia.EDU (Cameron Randale Bass)
Newsgroups: sci.physics
Subject: Re: Opalescence
Date: 15 Oct 92 16:48:26 GMT
Organization: University of Virginia

In article <1992Oct15.053722.13377@galois.mit.edu> jbaez@riesz.mit.edu (John C. Baez) writes:
>In article <1992Oct15.033402.12388@galois.mit.edu> jbaez@riesz.mit.edu (John C. Baez) writes:
>>(This "absorb and re-emit" scenario might actually be what's going on
>>in opalescence, but I'm not sure.  I'm pretty sure something along these lines
>>occurs in luminescence, e.g. dayglo paint.  But these are very different
>>from transparency.)  
>
>I meant fluorescence, not luminescence.  Anyone knowledgeable willing to
>divagate on fluorescence, luminescence, opalescence, and
>phosphorescence?   Actually it's opalescence that's the most mysterious
>to me.  Hmm, opalescence may be the answer to a question Dale Bass recently
>asked me: what would happen if light had to fight its way through lumps
>much bigger than atoms?

     Actually the question ran (beginning of question):

     I agree, but having a couple of hours to think about this, I 
     am not sure what would happen an the incident wave (or alternatively
     the incident photons) if the medium were fractions of a wavelength 
     in dimensions but still very much larger than a molecule.  
     Would a portion of the incident wave be extinguished
     with some characteristic length as very many people seem to assume, 
     or would all of it be snuffed at the boundary dipoles as the 
     equations (and Born) seem to say?

     I wonder if the characteristic snuffing distance is molecular
     or macroscopic?  Any opinions?

     (end of question)

     In other words, at what point can an incoming wave be considered
     extinguished in a dielectric medium?  The use of Heisenberg
     uncertainty seems to imply that one cannot detect a change in 
     wavelength until 

                    2 pi L / delta lambda ~ 1

     where L is the distance and delta lambda is the wavelength shift.
     This implies for a medium of refractive index n that the distance 
     over which a phase shift of 1 radian will be detectable is 

                    X ~ lambda / 2 pi (n - 1).

     This, however, can be huge depending on n and lambda.  However,
     the very nice equations provided by Born imply that the wave is
     extinguished *everywhere* within the medium by the boundary
     dipoles.  I believe that Born and Wolf actually state that this
     is the case.

     My question sought to distinguish whether this extinction distance
     was molecular (as implied by Born and the relevant equations),
     or macroscopic (as seemingly implied by Heisenberg), and what
     one might see if one put a macroscopic dielectric of sub-wavelength
     width in the path of an incident plane wave.

     Any experts on dispersion theory around?

                           dale bass

-- 
C. R. Bass                                           crb7q@virginia.edu
Department of Mechanical and Aerospace Engineering
University of Virginia
Charlottesville, Virginia                            (804) 924-7926
Organization: Carnegie Mellon, Pittsburgh, PA