From: pcdhSpamMeSenseless@electrooptical.net   
      
   On 2019-12-20 13:05, ggherold@gmail.com wrote:   
   > On Wednesday, December 18, 2019 at 11:17:49 AM UTC-5, adamstr...@gmail.com   
   wrote:   
   >> I'm trying to form a gray-scale image of a scene by scanning it with a   
   laser in daylight.   
   >>   
   >> The setup is, I stare at the entire scene with a stationary lens and a   
   single photodetector (and this does not scan, but takes in the entire scene),   
   and then I scan a laser spot across the scene to build up a rastered image.   
   >> The light contribution from the entire background is 8000X brighter than   
   the light from the laser spot.   
   >> I have heard that it is possible to extract faint signals from a noisy   
   background by modulating the signal (the laser spot) and extracting the   
   matching frequency components from the noise, which sounds crazy to me   
   because, well, the noise is 8000X    
   greater than the signal, and any detector is going to have a hard time seeing,   
   say, 1000 photons on top of 8,000,000.   
   >>   
   >> What am I missing?  I'm not a signal-processing guy, if that wasn't obvious   
   already.   
   >>   
   >> Can modulating the laser spot enable me to build up a grayscale image of   
   the scene, and if so, how, or should I take a different approach?   
   >   
   > A narrow band pass filter (Interference filter) centered on the laser   
   > wavelength would help a lot. (maybe you already have one?)   
   > Seems like there will alos be a distance effect in the reflected laser   
   > light.  Objects twice as far away will only scatter 1/4 the photons   
   > into your detector.... maybe that's what you want?   
   >   
   > George H.   
   >   
      
   If the filter is on a flat surface, angle tuning will limit the FOV, though.   
      
   Cheers   
      
   Phil Hobbs   
      
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   Dr Philip C D Hobbs   
   Principal Consultant   
   ElectroOptical Innovations LLC / Hobbs ElectroOptics   
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