I thought it could be just for a moment, or a few seconds, like a camera flash, but is the large energy consumption because you'd need a long exposure, and thus, you'd need to run the laser for a super long time, to get an image?

If trans-Neptunian objects are too dim to see with most telescopes, why is it not an option to just... light them up? Wouldn't a powerful laser from Earth be able to illuminate a small corner of the sky for observation?