RichD  wrote:   
   > > In an anisotropic medium, there are still plane wave solutions   
   > > [i.e. something times exp(i k dot x - omega t) ].  However,   
   > > due to the anisotropic electric and magnetic susceptibility,   
   > > E and/or H aren't orthogonal to _k_.  That means that E cross   
   > > H doesn't lie along _k_, so the Poynting vector (energy   
   > > propagation) is in a different direction from _k_ (phase   
   > > propagation).   
      
   > OK, I think I get the idea: the wave propagates as   
   > usual, but Poynting points in a different direction.   
      
   At this point it might be useful to think more carefully about   
   what you think `the wave' is. You might prefer to think of the   
   energy flow (Poynting) as the thing that propagates, and the   
   (presumably) oscillating fields as merely a pattern which   
   in some circumstances appears to travel in a direction not   
   parallel to the energy/wave.   
      
   FWIW, it is possible to design (but perhaps not build) a medium   
   where the energy flows in helices about a chosen axis, but the   
   wave vector (`pattern') is parallel to that axis.   
      
   Also, which Poynting vector might you mean? :) arXiv:0908.1721   
      
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   Dr. Paul Kinsler   
      
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