[Laser] Re:: heliograph vs. laser indeed!

[F1AVYopto at aol.com]

>It is like for the radio and the antennas  directivity.
>The parabola size determines the beam angle because the  refraction 
>effects.
>With a perfect parabola the -3dB beam angle  is about = 70 x 
(wavelength / Diameter) 
>A 1 meter perfect  parabolic mirror gives with a 1 micron infrared laser 
: 
>= 70 (10^-6  / 1)
>= 7 . 10^-5
>= 0,000070
>70 microradians !  

>  That might be for radio wavelengths not much smaller  than the 
>paerture, but for vavelengths much smaller as in optical, the  beamwidth is 
>about wavelength/aperture, so 650nm/6.5 cm will give 10  microradians, or 
>about 2 arcsec beamwidth.  This is also a way to  expreass the resolution 
>of a telescope.

I have checked your  relation wavelength / aperture ratio as beam angle that 
seemed to me too  optimistic.
In the moon laser ranging at CERGA in France the telescope is a  1,5 m one in 
diameter and 20 m focal lens.
The best beam it produces is 0,64  arc second or (2pi / 1296000) x 0,64 = 
0,000003 radiant or 3 microradians.
If  I apply your calculation for a 1 micron wave length laser, 1000 nm / 150 
cm will  give 0,6 microradians that is very best but I think the laser 
emitting area and  its initial divergence are also active parameters.

I found your laser  link on the "microlaunchers" site at  :
http://www.microlaunchers.com/7407site/L3/laser/laser-link.html 
It is a  very ambitious project !
The aiming stability with the earth cressant  tracking will be a real 
challenge !
Thank you again for all the info.
73  Yves F1AVY