Re: Laser protection

Wasn't it MacFraggin who wrote:
>> I can't find the equations for the dispersion of laser beams, but I
>> would have thought that at a distance of 300km the beam would so wide
>> that it wouldn't make an effective weapon even against black targets.
>
>(Assuming you mean 300.000km or 1 lightsecond):

In my country "." is a decimal point, so I thought you were talking 
about 300km.

>That depends on the wavelength of the laser. Diffraction increases
>directly pro****tional to wavelength, and decreases with lens size. An
>(infra)red laser will paint a huge area where an UV or Xray laser will
>still be focused to a few centimetres.
>If you have a big enough ****p, you might use huge lenses, but these
>will of course be inviting targets.

I've got this vague recollection that the laser that's used to measure 
the distance to the Moon (using the laser reflector left by the Apollo 
guys) produces a spot that's several kilometres across at a distance of 
around 380000km, and that's using a 3.5 metre mirror.

If my memory is correct[1] then if you tried to use that as a weapon, it 
would kill a light aircraft flying over Apache Point (they have to make 
certain that there are none in the area before firing) but would cause 
no damage whatsoever to structures on the Moon.

[1] I've tried lots of variations of Google search terms, but I can't 
find any site that tells me the information or how to calculate it that 
doesn't require a paid subscription to read the technical papers.

-- 
Mike Williams
Gentleman of Leisure