Nanopulse edged weapon

Nanopulse Edged Weapons are melee weapons specially modified with Nanopulse Laser Technology, which was patented by Harcourt Fenton Muddin the 22nd century. Unlikea normal weapon, the blade of a Nanopulse Edge weapon is made of plasma that is constatly energized by nanopulse lasers. When not in use, the weapon enters a power-saver state, with the blade de-activated.

They are featured in Star Trek Online

Reference: http://www.stowiki.org/Special_Weapons_Dealer