But this implausible design would take the fun out of the laser, reducing its efficiency as an omnidirectional weapon and making it more difficult to use or carry around. We went to Dr. Marc Nantel of Photonics Research Ontario for some other ideas. Nantel is the head of the Laser Micromachining Facility at Photonics Research Ontario a government funded research institute. His work involves cutting objects by focusing laser beams on them. Nantel agrees that a laser sword without a fixed length could be a bit of a liability.
Laser beams are parallel rays of light - they'll go very far at the same intensity.
If you put a lens in the way, you can bend the rays of light so that they converge to a focal point. After that the rays start diverging. The intensity will get weaker and weaker the further you go from your focus. Nantel explains that you can get more intensity from the same laser when you converge on a single point rather than simply beam parallel rays. Nantel himself uses a 12 watt laser that has to be tightly focused on the object he is cutting.