Anyway, it's scientifically impossible to make a lightsaber out
of a laser beam. As far as I know, there is no energy field that
can trap photons... the lightsaber blade will simply shoot out to
infinity and will pass through another blade.
Using plasma would theoretically be possible... an electromagnetic
field can trap the ions in the plasma. Heck, Cherenkov radiation
would give the trapped plasma a bluish glow.
The difficult part about using plasma would be the engineering
aspect... it takes a lot of energy to heat matter into the plasma
state, and it would be very difficult to shape the electromagnetic
field such that it can trap the plasma into the shape of a
lightsaber blade.
