From: r_delaney2001@yahoo.com   
      
   On August 22,  Skywise wrote:   
   >>> Lasers are useful for their low dispersion.   
   >>> What I wonder is, why are they necessary for the   
   >>> most common applications?  e.g. bar codes, CD readers,   
   >>> My point is that collimated, non-coherent light   
   >>> was developed long before the laser.   
   >   
   >> Sure, starlight for instance.  The problem with spatially incoherent   
   >> sources such as LEDs and tungsten lamps is that in order to get a small   
   >> focused spot, you have to trade away almost all of your light.   
   >   
   > Am I remembering correctly that the output from a laser is   
   > 'appears' as a point source? And from that you can "get a small   
   > focused spot" WITHOUT "[trading] away almost all of your light".   
      
   I'm still unclear - if a light source is focused and   
   collimated into a tight beam, where is the light "traded away"?   
      
   I recall working on a photolithography project once, with   
   a mercury arc lamp source, a series of (very expensive)   
   lenses focused the light, worked fine.  Nobody mentioned   
   anything about using a laser for greater efficiency.  As   
   you can suss from my questions, I wasn't on the optical team -   
      
   --   
   Rich   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)