[Laser] laser optics questions

[Tim Toast]

Hi all,
I just want to be clear, i'm not trying to argue one method is 
better than some other here. From what i've read about all this 
so far, it looks like most, if not all, of the de-coherence noise 
is generated in the first kilometer or two as the spatial 
coherence of the laser is being destroyed by passage through 
the atmosphere. The de-coherence process has, in effect, 
modulated the beam in amplitude and so the beam carries this 
noise with it to the detector. 

I suspect an LED still suffers from some scintillation because of 
its narrow bandwidth. Both the laser and LED have a finite 
bandwidth and so both have a degree of "coherence" which shows up 
as the noise and scintillation on both signals - the LED having 
less because its bandwidth is greater and has less temporal 
coherence. (Not because it has None) In the real world, no 
light source can be made "non-coherent" or infinite bandwidth.

I pick a random point in the discussion and run with it now... 
I don't think a fresnel lens would scatter laser light any more 
than it does with LED light. It may be that it is just more notifiable with a laser because it is a sharply defined 
reflection or scatter (caustic?). The LED light gets scattered 
just as much but its reflections are fuzzy and diffuse due to 
the wider bandwidth.

-toast