A few shots from the Pulse Cannon about to hit Samus.
The Pulse Cannon is a "variable" beam weapon used by Pirate Commandoes in Metroid Prime 2: Echoes. Pulse Cannon shots appear as blue energy projectiles (not unlike that of Phazon) and do minor damage to Samus. It is best for Samus to strafe or dash away from these attacks while concentrating return fire on the attacking Commando.
The Pulse Cannon is presumably a more advanced version of the Galvanic Accelerator Cannons used by the Space Pirates on Tallon IV. When Commandoes are taken by the Ing and become Darklings, their Pulse Cannons are augmented with dark energy.