From: pcdhobbs@gmail.com   
      
   >Is it possible for a photodiode to sense a laser beam from a very short   
   distance   
   > when the laser beam is not directed, to the photodiode itself. The   
   photodiode is placed   
   >just 1 inch from the laser beam, perpendicular to the laser beam in a dark   
   room, so will the scattering by the air be enough   
   >for the photodiode to sense that laser? There are dust particles in the air,   
   >but not much.   
      
   >Tech specs of laser are:- Max output <1mW Wavelength 532nm +_10   
   >Class II laser product.   
      
   Yes. That's more or less how most aerosol particle counters work. The light   
   pulses you get aren't very large, so you need good baffles and light   
   shielding. You also need a well-designed front end amplifier.   
      
   It's easier if you use a spherical mirror to collect more of the light.   
      
   Cheers   
      
   Phil Hobbs   
      
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