Laser Blade (3.5e Equipment)
From D&D Wiki
Laser Blade: A laser blade weapon has no blade until activated, its damaging end formed out of light and resembling a lightsaber. Its damage changes to typeless. When making a called shot, on a natural 20 you may sever the struck body part. Like vorpal, creatures immune to critical hits are not killed by the loss of a head, though a loss of an arm or leg may apply appropriate penalties. The laser part of the weapon is retracted when not in use, only leaving a handle. It can only be applied to piercing or slashing weapons.