[url=http://en.wikipedia.org/wiki/Boeing_YAL-1]

600KM doesn't seem like short range to me, and in science fiction, much more powerful generators are assumed. To provide more energy to the general populace and for much more power arduous tasks. So in a ship that's like, twice as tall as this thing is long, and ten times as long as this thing is. I think you could put a SUBSTANTIAL amount of energy into a single rotary mounted laser.