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

[Tim Toast]

thanks for doing the math Yves!
wow, i didn't expect a problem with a collimator being too
small..  so it looks like a 5 milliwatt laser can equal the
brightness of a 1 kw heliograph at 200km, IF the laser can
be collimated to 20 microradians (3.8 meter spot). But, it
would require a collimator lens or mirror diameter more
than 1 meter to accomplish. So the heliograph wins! The
math always seems to bring up interesting and sometimes
un-expected results... 

I was wondering how you find the maximum collimation
capability for a given diameter lens or mirror. That can
give an idea of the maximum results we can expect from our
optics. It would also be interesting to see the figures for
fresnels to compare with glass lenses.

That's interesting about the 10 watt array of Luxeons on
the moon collimated to cover one whole hemisphere of earth
(2 degrees), it would be PGP detectable with 30cm (12 inch)
telescopes? awesome! 

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)





       
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