On Wednesday, August 26, 2015 at 3:21:27 PM UTC-4, RichD wrote:   
   > 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   
      
   And how big was the focused spot size of the lamp?   
   And then tell me the intensity   
   (in watts/ cm^2 or some-such units)   
      
   Mind you I have nothing against lamps,   
   (optical pumping uses an rf discharge lamp,   
   lots of Rb with a little Xenon.)   
      
   George H.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)