Re: Can Photoelectric beams work underwater and what would the maximum distance

Peter:

Water will scatter and absorb light photons just as air does.  There is 
nothing about the photoelectric process that would preclude it from use 
in a water medium.  The greatest distance it could be used would depend 
on the intensity of the light source and the absorption and scattering 
qualities of the water between the source and the detector.  A 
photoelectric beam would have a shorter useful distance in very dirty 
water than it would in clean, clear water.

Coherent light, such as from a laser, or use of focusing lenses would be 
useful in increasing the useful distance.

I hope this helps.  Please feel free to write back if you have any 
further questions.