As promising as laser powder bed fusion has been in aerospace manufacturing, the technique has a downside. Bubbles of gas in molten material can leave voids, called “pores,” hidden inside the walls of metal parts. This kind of defect is annoying for noncritical parts such as air-conditioning brackets, but unacceptable for critical parts, such as components of engines, because they can lead to cracking. The mystery of how and why pores form is beginning to lift, largely because of a microscopic imaging technique applied by UVA professor Tao Sun and his team.