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

[Charles Pooley]

  F1AVY wrote:   
  
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 invite people to check my math in the Laser Link article in my 
website.
  
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>At any rate, all this goes a long way toward understanding
>the minimum power densities required for detection with a
>given sized lens or telescope, and transmit power / beam
>divergence etc.. maybe math isn't so bad after all 8)

  If you can count photons, that's as good as it gets, and there are 
ways to do that.
  
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Math often describes ideal properties but, as explain Charles Pooley 
KD6HKU 
in his last mail, the laser diodes are not perfect sources and have 
many 
aberrations.
For example a powerful infrared laser diode has its active output area 
like 
a thin rectangle 1 micron x 200 microns. 
The spot on a target is a rectangle with astigmatism and focusing 
problems.
As explain Charles theses problems can be reduced by a cylindrical lens 
or 
worst by a slot diaphragm that gives enormous losses.
  -------------------
  With suitable optics, diode lasers are capable of diffraction limited 
resolution--fairly easy for the 30 mw and under with a narrow chip.
  
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  Charles, I find many info about your "microlaunchers" but can you 
give us th
e link to go directly to your small optical space data link using 7 cm 
transmitter optics and a 30 mw 650 nm laser.
  --------------------
  
  Just go to home page, then "MORE", "initial proposed spacecraft 
design", then "Laser Link"
   
  I'd put the url here but I think this forum rejects it--that's why I 
said microlaunchers(dot)com.
  
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  Besides the optical mouse IC to track the earth relative movement is 
a fantastic idea !
  --------------------
  
Thank you-- that's an example of "defensive publication"  If I can't afford to 
patent it now, but don't want anyone else to, it gets published.  I had a 
year in US to file, but no one else can.  It became public domain.
   
  Charles Pooley  KD6HKU
   
  BTW, there's a Youtube intro video (2 minutes)--just use tag word 
microlaunchers.  Also on Google and Yahoo.