From: jos.bergervoet@xs4all.nl   
      
   On 20/04/17 9:02 PM, benj wrote:   
   > On 4/15/2020 3:49 AM, Ned Latham wrote:   
   >> I was thinking about parallel-sided glass blocks, and their   
   >> fascinating demonstration of refraction of light on both   
   >> entry and exit, and it occurred to me that I've never seen   
   >> or heard anything about the beam itself except that it's a   
   >> little wider on exit than on entry.   
   >>   
   >> So I wondered: has anyone ever looked at the exit beam in   
   >> sufficient detail to detect a spectrum or dismiss the idea?   
   >   
   > Why would you assume exit beam is wider?  What if it's focusing down?   
      
   If it was already a converging beam when entering the glass, it might   
   still be after exiting (unless it passed its focus point somewhere   
   inside the block.) So I think that meant here is a parallel beam   
   entering (but a parallel beam is an idealization, so the question   
   is not completely clear).   
      
   > Consider a laser beam through the block,   
      
   How the beam is created can be left out of it (but 'monochromatic'   
   would help to simplify things perhaps, although the shape question   
   then still stands.)   
      
   >    When you say looked at in great   
   > detail what do you mean "great"?   
      
   Exactly, benj. There is a number of increasingly accurate approximations   
   in physiscs, starting from geometrical optics (simple ray tracing, in   
   which case a perfect parallel beam is possible and will remain perfect),   
   then going to geometrical theory of diffraction, physical theory of   
   diffraction, full Maxwell equations, and Quantum Electrodynamics. If   
   needed even extended with weak and strong-force corrections (or else   
   the electron has the wrong electromagnetic moment so the propagation   
   of light will still be described with a slight error)   
      
   >     Generally the progress of say a single   
   > mode laser beam through a material can be theoretically calculated to a   
   > great deal of accuracy.   
      
   True, but since the block of material is cosidered large here (I think)   
   there is no wave guide with discretized 'modes' and a continuum of   
   possible wave fronts exists.   
      
   >    Not saying there might not be some interesting   
   > details found but generally classic theory is usually highly in   
   > agreement with measurements.   
      
   The full Maxwell equations will indeed be the most usefull tool here.   
   The description is in fact nothing else than light passing through a   
   window (a widely spread application of parallel-sided blocks of glass.)   
      
   --   
   Jos   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)