The vacuum chamber is likely aluminum. Tin melts at 232 C, aluminum at 660 C. Vaporizing the tin could require enough power in the laser to melt the aluminum. I

The vacuum chamber is likely aluminum. Tin melts at 232 C, aluminum at 660 C. Vaporizing the tin could require enough power in the laser to melt the aluminum. It seems feasible to me, anyway, and is certainly sounds like the kind of thing that happens in equipment development.