Special forces have been field testing a 'Plasma Knife'. That is right, a real life plasma knife. Do not think 'light saber' though, it cuts using glowing hot ionized gas. They say it is not used for a weapon but as a medial tool. The advantage of the plasma knife is that by its nature it cauterizes and sterilized the wound.
Seriously though, not a weapon? I have a hard time believing it will not eventually be used as a weapon.
"Special Operations Command have “completed ongoing testing and field evaluation studies” of the next best thing, according to a Pentagon budget document. It’s a Plasma Knife which cuts through flesh with a “blade” of glowing ionized gas. But rather than being a weapon, the Plasma Knife is a surgical instrument that could save lives."