XPost: alt.lasers   
      
   Salmon Egg  wrote:   
   > but it was possible to have interactions when phase and group   
   > velocities were in opposite directions.   
      
   And quite a popular subject these days it is too :-)   
      
   --   
   ---------------------------------+---------------------------------   
   Dr. Paul Kinsler   
   Blackett Laboratory (Photonics)   (ph) +44-20-759-47734 (fax) 47714   
   Imperial College London,          Dr.Paul.Kinsler@physics.org   
   SW7 2AZ, United Kingdom.          http://www.qols.ph.ic.ac.uk/~kinsle/   
      
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