[Laser] coherence and scintillation

[C. Turner]

Over the past several months, I've done some semi-scientific comparisons 
of coherent light versus noncoherent light, using the same apertures for 
both receive and transmit over a 15 mile path.

Some details may be seen here:

http://ka7oei.com/Coherent_versus_noncoherent_test.html

These experimental comparisons were done using a standard, cheap red 
Laser pointer module (from a $3 Laser level) and a Radio Shack 
high-brightness red LED, both of which being Pulse-width modulated.  The 
intent was to determine, empirically, what the difference would be, 
given that everything was the same - except the spectral width of the 
light source.

As can be seen from the results, Lasers have certain drawbacks when it 
comes to the experiencing of scintillatory effects.  It is also worth 
mentioning that the beamwidth of the laser was *not* really an issue in 
this case as "beam wander" was a probably a negligible factor in this 
experiment:  This was seemingly verified by "walking the beam" on the 
far end to determine the spot size and noting that its cutoff was well 
beyond the receive aperture, as well as noting that at the beam edges, 
the rate of beam dropoff was quite dramatic (e.g. two steps further, 
there's no sign of the beam.)

73,

Clint
KA7OEI