It isn't a normal laser, it is a gravity laser. The gravity laser compresses all of the matter in the way to the point where fusion occurs between all elements. This lets you poke a whole through the planet since the beam can get past the matter it has already compressed. While the beam is still on it will be pulling more and more of the planet into it. When you get enough captured in the beam, turn it off and left the compressed matter explodes via nuclear fusion.