camera_lumina at hotmail.com
Fri Nov 1 13:43:36 PST 2002
"Some of these problems can be avoided by using very short pulses.
Again you get into dwell, the short pulses -must- be made up for by
increasing the PRR and this defeats the who purpose of the short pulses
since you need more of them (we're talking an integration effect here
so it doesn't take much to understand why duty cycle isn't as important
as you make it out to be"
IR is not particularly better than visible for most wavelengths, and fog is
the real killer (as opposed to rain or even snow). But I know the LIDAR
folks found that there ARE some nicer wavelength windows within the IR band.
As for pulsed lasers, here's where my knowledge of military applications
fails me (I used to work in civilian ultrafast/femtosecond optics.) As for
pulsing such a laser, I can't quite imagine WHY this would be attempted for
damage reasons (reconaissance is a different sotry). If the pulsing is in
the millisecond regime or faster, I would imagine this is only to allow for
population re-inversion of the laser material (ie, to keep it lasing at
higher peak power). But I assume the military's laser research in the
wavelengths of interest are well beyond the need for this.
Of course, there's the easy possibility that the military does use fast
pulses for the purpose of knocking out certain sensor materials via 2nd
order/nonlinear processes. As we found out back in 92 or so (from some
declassification), the military's optical research in Adaptive optics was in
some ways 30 years ahead of the civilian world. Who the heck knows what
they're doing with laser pulses.
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