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SCIENCE

Build Your Own Ray Gun
Brian Runciman

On Building the
personal hand-held integrated light actuated neon defence energy rifle

Lasers or Light Amplification by Stimulated Emission of Radiation. We all know about them: they run our CD players, gaze into our eyes, perform minor surgery, act as high tech pointers in lectures, oh, and DESTROY ALL BEFORE THEM. At least, that’s what Reagan wanted, and who can blame him? He’d seen Star Wars and, with touching originality, named a government program after it.

Who can decide what to call these things? Laser guns, phasers, ray guns, beam weapons, blaster rays, disintegrators, and on and on and on. What we really need is a marketing focus group to brainstorm a really catchy, commercially viable moniker for the personal hand-held integrated light actuated neon defence energy rifle – mmm, PHILANDER is not the family oriented image we need for such a useful domestic appliance. Especially as people who use the weapon would be PHILANDERers.

Still, let’s bike our suggestions over to Dominic and Harvey at the agency, they’ll come up with something…
Perhaps for personal defence there is something rather attractive about a non-lethal means of disabling a naughty person. We have the Taser, of course, but a laser weapon, factory-set to stun, could actually be quite useful for any number of things: law enforcement, nervous pedestrians in dodgy areas and, of course, having a laugh. And there is the problem; no sooner is the first PHILANDER on the market than some criminally inclined school kids get hold of one and render their physical education teacher insensible, or should I say unconscious, most being insensible already.

That’s what I would have done, hating rugby as I did: the problem is that every denizen of the educational system has his or her particularly hated subject and they run the full gamut. That means that by first break every teacher in the establishment would be comatose…on the other hand, who could tell?
So, here’s the science bit, as Jennifer ‘Rachel’ Aniston so memorably said while flicking her eponymous hairstyle a couple of years back. Anything that produces light does so through electrons changing orbit and releasing photons–the reduction of an electron’s energy level to a ground state from an excited state produces light. Usually this happens randomly–the light could be pulsed in any direction. However, Einstein (he crops up all over the place, doesn’t he?) realised that if a photon hits an atom that is already excited it releases a new photon that is identical to the incoming photon, producing an effect called "stimulated emission". Really a sort of cloning which amplifies the number of photons.

This all happens in the controlled lasing medium of a laser, which is pumped so that many atoms get excited electrons, increasing the ‘population inversion’, which is the number of atoms in the higher energy state against those in the ground state.
So, because in laser light all the ‘crests and troughs’ of the wave line up with each other and all travel in the same direction it is much more ordered than ordinary common or garden light. The orderly nature of lasers gives us the ability to control it for precision applications, and means that it is more powerful, as it can be focused more efficiently.
If we were talking potential weapons then the best bet are CO2 lasers, because they emit in the infrared and microwave region of the spectrum. As infrared is basically heat these lasers can melt the materials they are focused on, even cutting steel and are even capable, some say, of heating a pot noodle evenly.

Where does that leave us in the personal ray gun stakes? Well you might as well get a laser pointer because lasers with any significant power are pretty big. Even if they could be made at a portable size then we are still restricted to giving somebody a mild case of sunburn and not a lot else. In the long run it may be that giving any potential attacker a case of sunburn may be sufficient–even criminals want to look their best in this image obsessed world–and skin cancer doesn’t look good on anyone.

As far as space-borne lasers go, ostensibly this seems a lot more likely, there being less in the way of size and weight restrictions in outer space. Fortunately even the stimulated emissions of lasers lose their coherence over a relatively short distance. After only a few hundred miles we’re back to tanning strength only. So, unless any government wants to undertake a mass program of melanoma induction in an enemy territory, we’re not going to see any scenes from Independence Day replayed (thank goodness).
On the personal level, then, if you must PHILANDER I’d recommend you start working out to enable you to carry the kit. But, of course, if you work out to that extent nobody is going to bother you anyway…


© Brian Runciman May 2003
brunciman@hq.bcs.org.uk
In-house Editor
The British Computer Society
www.bcs.org

Brian Runciman writes about science for Hacks from time to time.

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