Suppose you have a turbid media - consisting of targets embedded in a   
   scattering media. Examples include sonar situations, blood samples, and   
   biological tissue.   
      
   The question is, regarding relatively large targets inside the media, the   
   targets   
   being more absorptive than the scatterers, this could be 15 micron parasites   
   floating in blood with rbc scatterers...They have a 1% volume fraction, so on   
    average, a shot through the axis (transversely will hit one, roughly.   
      
      
   Considering that the blood is traveling in an arteriole of 1mm dia, and that a   
   red diode laser is aimed transversely through it to a PD, here are options   
   to get SNR. In this case, the scattered light and the bright field back ground   
    are the chief sources of noise, as far as I can foretell.   
      
   Here seem to be possible ways to get the SNR up. (and granted this may not be   
    possible.) They are:   
      
   -narrowing down beam for a bulk PD measurement, so that the collimated beam   
   subtends a major portion of the PD area. (I have a Vishay ,23 mm2)   
      
   -using a lens system   
      
   -using a cmos imaging array   
      
   -using polarization to select non-scattered rays   
      
   -speckle? scattering measurement?   
      
   The above seem to be the main tools to improve snr - Put many photons through   
   at   
   one side and hope that enough make it through with minimal scattering. These   
   signal photons will then give a measure of the parasites. In the meantime, the   
   highly scattered photons are minimized by geometrical filtering, including   
   small area, collimated beam, lens, or cmos. The cmos sensor has a small area   
   (25 microns2), which probably needs a lens.   
   ?   
      
   jb   
      
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