Beamers are similiar to Lasers, but fire longer bursts of less intense coherent light. The net energy output is much greater, but spread over a longer period. This means that the gasses created on impact do not explode in a surface explosion. Instead, the laser tunnels into the material, and only when the tunnel becomes deep enough that the gasses can no longer be vented does it cause an explosion. This occurs inside the armor plate, greatly assisting penetration.
This is a development of the regular laser that uses a lot more energy without inflicting more damage on non-armored targets. Improved batteries make up for the greater power consumption, and heat is vented from the weapon by force-field technology. It is very popular with the military because of it's low overhead and significant effect, but has few civilian uses.