Where do you find the dark beam in Metroid Prime 2 Echoes?

Eventually you'll find your way blocked by some Black Doors in the Agon Wastes, and you can't find two more Dark Keys. So a transmission from U-Mos will come in telling you to retrieve stolen Luminoth gear. So go to the place in a Space Pirate Base, and you'll have to defeat Dark Samus 1. (Yeah, there's actually four, and they have their own section in your logbook.) So then you can enter the Dark World from a portal there and also get two more Keys and the Light Beam. And there you have it.