The experiment measured how much laser energy is absorbed during high-power laser welding. As the laser vaporizes metal, it can form a narrow keyhole cavity; reflected light and X-ray imaging help show how that cavity changes during processing.

I cleaned up a researcher-supplied diagram so the laser path, integrating sphere, reflected light, X-ray view, and keyhole inset were easier to follow. I also made a short GIF showing how reflectance changes during keyhole formation.