Ultrafast Electron Diffraction Reveals Laser Melting

Scientists at the University of Toronto have employed femtosecond electron diffraction to study the ultrafast melting of aluminum under illumination by 120-fs pulses of near-IR laser radiation. The electron technique promises to enable investigations into photoinduced dynamics, with applications in condensed-phase processes, surface chemistry and time-resolved

In the work, the researchers collected transmission electron diffraction measurements on 20-nm-thick films of polycrystalline aluminum that were exposed to pulses of 775-nm laser radiation at a fluence of 70 mJ/cm². A 30-keV electron gun produced the 600-fs probe pulses, and a CCD camera imaged at 500-fs intervals the diffraction patterns that were generated on a microchannel plate/phosphor screen. By 3.5 ps into the experiment, the diffraction pattern had changed from a series of rings indicative of the face-centered cubic structure of the solid material to a single, broad ring characteristic of a liquid.