[Laser] 21 mile daytime laser contact durin ARRL 10GHz & Up contest

[Kerry Banke]

Yves - This is very intereresting to me that you have also noticed reduced scintillation when using a filter. It may very well be due to  one of the other reasons you state. It could be interesting to try some form of translucent material in place of the filter to see if maybe it is due an averaging effect.
   - Kerry N6IZW - 

F1AVYopto at aol.com wrote:
  Kerry
A star is a punctual source but it is also a not coherent and not 
monochromatic source.
With a laser the scintillation is a very complex problem.
It is not only an erratic convergence modulation with angular micro 
displacements associated with beam global intensity fluctuations.
Constructive and deconstructive phase combinations give beats that occur 
into the photo detector sensitive layer because micro light speed modulation due 
to air density fluctuations.
This beating effect gives a very deep granulation noise.
I suppose your multilayer dielectric filter is fitted in a conical beam just 
in front of your photo detector.
This mounting gives selective rings from the edge to the centre with a 
strong bandwidth enhancement.
With the monochromatic laser light it is possible the filter give a 
diffusing ring that reduces the scintillation by a certain averaging on the 
convergent area.
May be the spot motions are reduced?
May be the laser light coherence is partially lost after the filter because 
its obliquity?
Normally a filter has no effect on the scintillation by I had also noticed 
this effect and I cannot explain why?
73 Yves F1AVY






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