A powerful laser strikes a diamond like a sledgehammer, with matter itself serving as the anvil. The impact lasts only an instant but generates pressures a million times greater than atmospheric. Physicists have long dreamed of peering into that moment to see how atoms rearrange under the onslaught.

The X-ray beam here is like a camera flash. The trouble is that the brightness of the flash itself can vary from shot to shot. To avoid guesswork, the researchers devised a "built-in ruler": part of the beam passes through a narrow aperture (collimator) or a layer of stationary material. This signal serves as a reference, like a tuning fork for calibrating an instrument.

The method was tested on a diamond compressed by a shock wave to nearly 1 TPa. By comparing X-ray images of the hot, compressed diamond with a cold reference, the scientists accounted for thermal vibrations of the atoms — which weaken the signal. This allowed them to precisely measure how the crystal lattice of carbon changes under extreme conditions.

This isn't just about setting records. Understanding how matter behaves at such pressures is crucial for modeling planetary interiors, creating new materials, and even for thermonuclear fusion — the very process that powers the stars. The X-ray flash now tells us more.