[linux-elitists] Must have free space lasers!

Eugene.Leitl@lrz.uni-muenchen.de Eugene.Leitl@lrz.uni-muenchen.de
Fri May 4 14:56:40 PDT 2001


"Mr.Bad" wrote:

>     BW> The absorbtion of higher frequencies is quite noticable. That
>     BW> is why you really can't see that far.
> 
> Say that again, to yourself, and determine if you really mean it.

Across the electromagnetic spectrum, there are several areas of
low absorbance, called atmospheric windows. In some areas of the spectrum
the atmosphere  is almost as opaque as a brick wall. If you're online, 
ask Google for atmospheric window wavelength and similiar keywords.
Wtf, have a gander at http://www.icess.ucsb.edu/geos/11121.html
It's transmittance, not adsorbance, though.
 
> Let me try this again: laser, communication, not line-of-sight. Could

Fata morgana. Okay, it's line of sight, but it's not line of sight.
It's sometimes line of sight. Fiber optics. Ditto. Mirrors. And smoke. 
Lots of smoke. Orbiting photonic delay line, preferably using
Bose-Einstein condensate. Did I already mention mirrors?

> you create a short-wave laser? How big would it be? How would you

About the shortest shortwave laser is x-Ray. It's about tabletop
sized. But the pumping laser is a bit bigger. Like, a lot bigger.

> encode information into the laser signal? What would happen to that

Try amplitude modululation. That's laser yodeling.

> signal if you were bouncing it off the atmosphere?

You can't bounce stuff off the atmosphere. You can bounce stuff off
an ionized atmosphere layer, though, the ionosphere.
 
> Spread spectrum... lasers?

Lasers are usually monochromatic (narrow wavelength) and coherent
(same phase). In theory, you could have pretty white lasers which 
are coherent. I have no idea how white a laser can be, but if I'd
want to build one I'd look into FEL (free electron lasers,
a kind of a coherent synchrotron lightsource, where an electron
beam in an open cavity passes through a wiggler, or undulator).

I don't think maser radiation would bounce off the ionosphere,
but that's strictly speculation.

Now I've ran out of my LFP stock, and it's all your fault.



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