A corner reflector. Now that's interesting, presumably something akin to reflectors used in some cameras and other optical equipment to see 'through the lens' when the eye isn't directly in line with it? Add another and you look at your own eye. How stupid of me not to think of that, particularly with my camara sitting right here by my computer. It would be a bummer to have a big laser foiled by a set of mirrors, or worse, turned back.
I'm still wondering about what would happen if a powerful laser hit a damaged mirror/reflector, though. I know people test lasers using well-made mirrors because the idea is to make the laser work- I'm just curious if anyone has tested a laser on a deliberately flawed mirror, since under field conditions a reflector might get damaged and be only partially reflective. If it loses too much of its reflective surface area, would it absorb the heat rather than reflect it, and possibly be damaged even more?
I am now wandering into the realm of speculation here. :) I have never been involved with laser mirror studies on the long term viability of defective or flawed mirrors. An optical physicist would be far more qualified to answer these questions. :)