Re: Mobile solid state laser gun

In article
<5daf6ab9-600f-4b09-b704-14bb5b82d754@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
Bob <bob.edwards@xxxxxxxxxxxxxxxxxx> wrote:

On Aug 20, 8:51 pm, Ignoramus15257 <ignoramus15...@NOSPAM.
15257.invalid> wrote:
On 2008-08-21, Larry Jaques <novalidaddress@di> wrote:





On Wed, 20 Aug 2008 12:05:49 -0500, with neither quill nor qualm,
Ignoramus15257 <ignoramus15...@xxxxxxxxxxxxxxxxxxxx> quickly quoth:

Picture is here

http://lenta.ru/news/2008/08/20/heltd/

Story is here

http://www.boeing.com/news/releases/2008/q3/080819a_nr.html

If it could quickly shoot down fast moving things such as artillery
shells, I think that it will be very revolutionary.

I want to know how many _satellite_ kills will happen as a result of
testing the lasers.  Um, OOPS!

The idea sounds like fun, but do not forget that energy per square
inch is the inverse of the square of distance. Ie, if the gun can
develop so much power at the distance of 1/2 mile, it can only develop
1/160,000 that power, per square inch, at the distance of 200
miles. And that does not even cound scattering of light and
absorption by atmosphere.


uhh, not quite!! The inverse square law applies to light radiating in
all directions, as if from a point source. A laser beam is highly
collimated and the energy per square inch is only subject to
scattering, absorption, and beam spread.

If for example, a 2mm beam spread to a 4mm diameter over some
distance, the energy per unit area would be reduced by a factor of 4
(plus whatever scattered or was absorbed). The distance over which
the spread occurs in immaterial. It could be a few inches or
thousands of miles.

Laser beams *are* subject to the inverse square law, once one is well
away from the nearfield (from the emitting aperture face to say 5 or 10
times the emitting aperture diameter). The "beam waist" is where the
transition from nearfield to farfield happens.

Google on "gaussian beam". There is too much material available.

Joe Gwinn
.

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