[Laser] AW: coherence and scintillation

[Jim Moss]

This scintillation effect is directly related to the beam width.
the beam width of a star is 360 deg!

If you increase the width of the laser starting at the source... (beam expander) you will deliver more energy to target (less dispersion) and if your beamsize is > than the disturbance cell you will have much less scintillation.

Jim
N9JIM


----- Original Message ----
From: "F1AVYopto at aol.com" <F1AVYopto at aol.com>
To: laser at mailman.qth.net
Sent: Friday, August 24, 2007 2:10:07 AM
Subject: Re: [Laser] AW: coherence and scintillation


Dieter
I agree about the global beam  coherence loss during a short travel in air 
but at the photodiode sensitive  layer scale the laser light stays perfectly 
monochromatic and has erratic phase  fluctuations at very small scale.
Kerry uses small photodiodes area with  small capacitance.
I experimented this receiving conditions with a red laser  to more 70 Km 
range and the scintillation is well stronger the one created by a  star near the 
same elevation.
When the convergent beam is adjusted not  exactly at the perfect focusing 
point on the photo detector I noticed the  scintillation decreases.
I noticed also if the laser is beamed on a  bouncing diffuse area the 
scintillation totally disappears on a RX beamed to  this bouncing area. 
A diffusing media fitted in front of the photodiode will  give losses but it 
is also possible it could reduce a little bit the  scintillation.
73 Yves F1AVY.  
http://pageperso.aol.fr/yvesf1avy/index.html  




   
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