The Hammer of Thor is, despite its name, an axe wielded by Eric the Red-Eye in the 1987-1996 animated TMNT TV series. It appears in the episode, Northern Lights Out.[1]
Eric refers to the weapon as the "Hammer of Thor" himself. The "hammer" is actually a holographic laser, and is destroyed by Donatello when he uses its own frequency to disrupt it. It is named after "Mjölnir", which in Norse mythology, is the hammer used by the deity of thunder, Thor.