From: neufeld@helios.physics.utoronto.ca (Christopher Neufeld)
Subject: Re: Laser weapons
Organization: University of Toronto Physics/Astronomy/CITA
Date: Wed, 2 Sep 1992 14:42:23 GMT

In article <rwallace.715424570@unix1.tcd.ie> rwallace@unix1.tcd.ie (russell wallace) writes:
>In <1992Sep1.213233.7293@spss.com> markrose@spss.com (Mark Rosenfelder) writes:
>
>>I'd like to throw some laser weapons into an sf story, but I find I don't
>>know enough about lasers.  
>
>>Some questions:
>>Are these things even practical as hand weapons?  
>>How much energy do they use?
>>Do they make a noise when fired?
>>Does the frequency matter?  I.e., would it make more sense to generate
>>  ultraviolet or gamma rays rather than visible light?
>
>Basically, lasers as we know them today are inherently useless as
>weapons - they don't put out enough power.
>
   Well, pocket HeNe's don't put out much power, but even fifteen years
ago a tabletop laser could put out a beam, a small fragment of which
reflected from a cracked lens could burn through clothes and burn the
skin underneath. I know somebody to whom this happened. Ruined a
perfectly good shirt and left some marks on his skin for a while. He
didn't even feel it at first, and the tracery on his skin showed how he
moved back and forth behind the table looking at the apparatus.
   There are lasers which could make you severely uncomfortable nowadays,
though the beam would have to sit on you for a large fraction of a second
before you expect serious damage. For instance, the forty foot CO2 laser
here at the Toronto Science Centre, built for Expo '67, can immediately
ignite wood placed at the focus of an IR lens. Cinder blocks take a while
to go through, but I would say that the focus of that laser is probably
about as healthy a place to be as the flame from an oxyacetylene torch.

>To get enough power from an energy weapon, you want to tap it directly
>from a nuclear reaction.
>
   Well, that's hardly necessary. You can do significant damage to a
person by dropping just a kilojoule of energy onto a small spot over a
short time interval. I believe flashlight batteries deliver more than
that much energy over their lifetimes.

>So the first practical energy weapon will probably be a fusion gun,
>using a fusion reaction to produce energy, arranged so that the energy
>is emitted from one end of the reactor. Whether the beam will primarily
>consist of charged particles, infrared, visible light or X-rays I don't
>know; it would depend on exactly how the device worked.
>
   David Drake has weapons of this description in some of his novels. I
believe he describes them in _Target_. It's supposed to be an inertial
confinement fusion reaction run with a hole in the reaction chamber. I'm
not convinced that it would be a very effective weapon in an atmosphere,
where we consider 'effective' to mean it does more damage to a target
twenty metres away than it does to the wielder.

>The only other viable idea for an energy weapon I've heard of is the
>X-ray laser powered by a nuclear bomb, suggested for the SDI project; a
>weapon that requires a nuclear explosion at the firer's end probably
>isn't what you're looking for though :-).
>
   That's the quick and easy laser gun. SDI did also consider visible
light chemical lasers using a hydrogen-fluorine power source.

>Russell Wallace, Trinity College, Dublin  rwallace@unix1.tcd.ie


-- 
 Christopher Neufeld....Just a graduate student  | Confidence is the feeling
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