Conversion Beamer
The Conversion Beamer is an Imperial antimatter weapon from the Dark Age of Technology.
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).