Conversion Beamer
The Conversion Beamer is an Imperial antimatter weapon from the Dark Age of Technology and fine example of the Good Shit.
Unlike traditional laser-based weapons; the beamer fires an energy beam that converts that matter of its target into pure, explosive energy. Thus, high-density targets like tanks or power-armored infantry would be instantly vaporized in a violent explosion upon contact with a conversion beam.
While powerful, its downside is that Conversion Beamers are incredibly heavy weapons, more so than the likes of the lascannon or heavy bolter, and the user must remain completely still for the beam to be effective while firing (not an easy feat in a universe where close combat is the norm). Additionally, now that AIs are illegal all the myriad preparatory and in-firing calculations necessary to keep the weapon from vaporising everything within a six mile radius have to be done by its user, which generally limits its use only to Techpriests, their Space Marine counterparts, and unusually ballsy Inquisitors with about thirty servo-skulls doing the heavy processing.