If you wanted to use a laser, here's how. To make a laser that cuts fit into a lightsaber handle and stop three feet away, use a laser pointer and magnify its power with ruby lenses or other laser media. In order to fix a lasers length, you need a focal point at which it burns the hottest. You're gonna have to do the math and figure out how many lenses you want to use plus the the amount of curvature to set the focal point in the right place to get a three-foot long blade. You would most likely have to run this laser through a gas medium yo make it visible, and you still have to envelope it in an EM field. The purpose of the field is to repel another saber. Simple elctromagnetics: like polarities repel. Without it, you would not be able to block a strike from another saber.

Also, light is electromagnetic in nature, coming in at a range of ~405 to ~790THz. High frequencies have a unique property - they can burn and even cut through steel. This property can be achieved through AC sinewaves. You can use high AC voltages and frequencies to create a plasma saber that cuts and repels other sabers - and contain all this power in a 30cm handle.

More about focal points: If you create a focal point, you have limited the length of the cutting portion of the laser. Create a focal point such that it cuts 18 inches behind that point, and 18 inches beyond that point (in an "X" shape until it dissipates. The cutting power of a laser is SEVERELY limited to a certain distance beyond that point. So you wouldn't be stopping the light, you would be stopping its cutting power. But if you go that route, you need to create a powerful EM field for the sabers to repel. However, to gain cutting power over a one meter distance requires trading that cutting power for distance and thus a proportionally hotter-burning laser. I personally will NOT use a laser in my saber design. Maybe at some point...if I did I would probably use some sort of solid state laser.