Light can destroy matter. Anyone who doubts this only needs to imagine what happens when a laser hits a copper wire seven times thinner than a human hair. The wire vaporizes instantly, creating a plasma several million degrees Celsius hot. Researchers at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) have now observed this very moment more precisely than ever before. Their results have been published in the journal Nature Communications.
Two lasers, one tiny wire
The scientists used two state-of-the-art lasers for their experiment. The first, a high-intensity optical laser called ReLaX, fires a pulse of light at the copper wire. This pulse lasts just 25 femtoseconds – or 25 quadrillionths of a second. In other words, one femtosecond is to one second as one second is to 32 million years. The pulse is so intense that it creates conditions otherwise found only near neutron stars. The wire vaporizes, and the copper atoms lose many of their electrons – they become ionized. This creates a hot plasma of charged particles.
A second laser, the X-ray free-electron laser at the European XFEL in Schenefeld near Hamburg, then captures snapshots of this plasma. It works like an extremely fast camera. "In our pump-probe experiment, we precisely measure the temporal evolution of this stimulated X-ray emission," says Dr. Lingen Huang, who led the experiments in HZDR’s High Energy Density department. "This allows us to determine how many Cu²²⁺ ions are present in the plasma at any given time." Cu²²⁺ refers to copper atoms that have lost exactly 22 electrons.
