<snip> 
> Couldn't you also use a high-power laser to vaporize the air in front of the
> particle beam? That might explain the fact you can see the beams from both
> the rifle and the Angel.
> 
>                                  Vaughn L.Porter
>                                   Not that you'd see the laser anyway...

I don't think it's possible to vaporize a gas... It's already
vaporized, you know... :)

A laser cuts things by heating them so much they evaporate. That's
what happens with metal, skin and whatever you put in front of it. But
if you heat up a bunch of air, the best it can do is expand a bit.
There's no way to make it disappear, because it keeps coming back.

It's kind of hard to explain the important points without giving a
lecture on Physics, so here goes:

  Light, lasers, X-rays, gamma rays, radio waves, microwaves - they're
all carried about by photons. Photons are closed packets of
electromagnetic waves.
  Each photon carries a certain amount of energy. 
  A laser has a very large number of photons concentrated in a very
small area, but the energy of each individual photon is small, most
times not even enough to ionize anything. That's why it's not too
dangerous to be close to a laser. The only thing it can do is heat up
stuff.
  Why can you see through air and not through a brick wall? Because
air, unlike most solid objects, is almost 100% transparent to photons.
So the laser just goes through, almost not heating up the air at all.
  Particle beams are altogether different. Each one of the particles
has a very high energy (because the particles have mass, and E=mc^2).
So, when one of the particles hits a molecule, it can tear it
completely apart and produce a shower of smaller particles in all
directions.
  The air is transparent to photons, but not to all particles. For
example, you don't get hurt by electricity unless you actually touch a
conductor, wich means air is not transparent for electrons.*
  Besides, for reasons somewhat obscure at this point (cross-sections
and things like that), it's much more likely for a massive particle to
hit an atom than for a photon, so a particle beam hits molecules much
more easily than a light beam.
  
Resuming: you can't use a laser to get the air out of the way, and you
can't use a particle beam unless you get the air out of the way.

Hope you didn't fall asleep...

   Tiago Sim$(D??(Bes

*Lightnings occur when the amount of electricity is enough to create a
stable electric current through the air, but this only happens because
"air" is not the only thing in the atmosphere. There's water vapor,
conductive dust particles, etc.