A laser melts metal powder layer by layer, and inside the boiling pool, vapor bubbles appear and collapse within milliseconds. Seeing this kitchen in action was previously impossible: the X-ray tomograph that takes 3D images is too slow. The sample has to rotate, and by the time it does, the melt has already changed a hundred times.

Engineers from Sweden found a way out. Instead of a single X-ray beam, they aimed three beams at the sample, spreading out like a fan. By rotating the sample at 25 revolutions per second, they capture three angles at once. A special program based on neural networks assembles a 3D image from these three flat pictures, just as the brain builds depth from two eyes.

The method was tested on melting alumina ceramics. The footage shows the melt pool stretching, with a vapor cavity pulsing inside it — the main culprit behind porosity in printed parts. Previously, these movements were smeared into a blur; now they're as sharp as in slow motion.

This X-ray "eye" could help tune lasers so that bubbles don't get trapped in the metal. That means parts for airplanes and implants will become stronger and more reliable.