Researchers capture strange behavior of laser-excited gold

New research, conducted at the Department of Energy’s National Accelerator Laboratory, SLAC, sheds light on the strange behavior of gold when zapped by high-energy laser pulses.

When certain materials, such as silicon, are subjected to intense laser excitation, they disintegrate quickly. But gold does the opposite: it becomes stronger and more durable. This is because the way gold atoms vibrate together – their phonon behavior – changes.

“Our results challenge previous knowledge by showing that, under certain conditions, metals like gold can become stronger rather than melting when subjected to intense laser pulses,” said researcher Adrien Descamps. at Queen’s University Belfast who led the research while he was a graduate. student at Stanford and SLAC. “This contrasts with semiconductors, which become unstable and melt.”

For decades, simulations have hinted at the possibility of this phenomenon, known as phonon hardening. Now, thanks to SLAC’s Linac Coherent Light Source (LCLS), researchers have finally shed light on this phonon hardening. The team published their results in Scientists progress.

“It has been a fascinating journey to see our theoretical predictions confirmed experimentally,” said collaborator Emma McBride, a researcher at Queen’s University Belfast who was previously a Panofsky Fellow in SLAC’s High Energy Density Science (HEDS) division. . “The precision with which we can now measure these phenomena at LCLS is astonishing and opens new possibilities for future research in materials science.”

In their experiment, the team targeted thin gold films with optical laser pulses on the Matter in Extreme Conditions experimental cage, then used ultrafast X-ray pulses from the LCLS to take atomic-level snapshots of the reaction of the material. This high-resolution glimpse into gold’s atomic world allowed researchers to observe subtle changes and capture the moment when its phonon energies increased, providing concrete evidence of phonon hardening.

“We used X-ray diffraction at LCLS to measure the structural response of gold to laser excitation,” McBride said. “This revealed information about atomic arrangements and stability under extreme conditions.”

Researchers found that when gold absorbs very high-energy optical laser pulses, the forces that hold its atoms together become stronger. This change causes atoms to vibrate more quickly, which can change how gold responds to heat and even affect the temperature at which it melts.

“This work resolves a long-standing question about ultrafast excitation of metals and shows that intense lasers can completely alternate the lattice response,” said Siegfried Glenzer, director of the High Energy Density Division at SLAC.

Researchers believe that similar phenomena could exist in other metals such as aluminum, copper and platinum. Further exploration could lead to a better understanding of how metals behave under extreme conditions, facilitating the development of more resilient materials.

“Looking ahead, we are excited about the possibility of applying these results to more practical applications, such as laser machining and materials manufacturing, where understanding these processes at the atomic level could lead to techniques and improved materials,” Descamps said. “We are also planning more experiments and hope to explore these phenomena on a wider range of materials. This is an exciting time for our field and we look forward to seeing where these discoveries take us.”