It doesn't shut itself off. It just stops cutting. It's like using concrete as a kitchen cutting board: that knife isn't going to do any damage, regardless of whether or not you stop pushing.
If you want to laser through metals, you need a different type of laser. Just as getting through concrete needs a different tool (say, a hammer chisel).
If you want to laser through metals, you need a different type of laser. Just as getting through concrete needs a different tool (say, a hammer chisel).