From: bret.cannon@invalid.invalid   
      
   wrote in message   
   news:67a52766-f7e3-413d-a2eb-40fa4cebfcca@googlegroups.com...   
      
      
   >   
   > Are you working with these forks for photo-acoustic spectroscopy that   
   > Frank   
   >   
   > Tittel's group at Rice University has been doing for about 15 years?   
   >   
   >   
   >   
   > Bret Cannon   
      
   The PAS sounds interesting. An interference effect or doppler?   
   Any references on?   
   JB   
      
   The PAS is generation of sound waves from modulated heating produced by   
   absorption of modulated modulated light.  This effect was discovered by   
   Alexander Graham Bell of telephone fame.  In the work of Tittel's group,   
   quartz tuning forks are used as very frequency selective and sensitive   
   microphones with a laser beam passing between the tines of the tuning fork,   
   which generates pressure waves that couple to the correct vibrational mode   
   of the tuning fork.   
      
   A Google search on "QEPAS" (Quartz enhanced photoacoustic spectroscopy)   
   turns up several references.   
      
   Bret Cannon   
      
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