Transient lattice deformations of crystals studied by means of ultrafast time-resolved x-ray and electron diffraction

Abstract

Ultrafast lattice deformation of tens to hundreds of nanometer thick metallic crystals, after femtosecond laser excitation, was measured directly using 8.04 keV subpicosecond x-ray and 59 keV femtosecond electron pulses. Coherent phonons were generated in both single crystal and polycrystalline films. Lattice compression was observed within the first few picoseconds after laser irradiation in single crystal aluminum, which was attributed to the generation of a blast force and the propagation of elastic waves. The different time scales of lattice heating for tens and hundreds nanometer thick films are clearly distinguished by electron and x-ray pulse diffraction. The electron and lattice heating due to ultrafast deposition of photon energy was simulated using the two-temperature model and the results agreed with experimental observations. This study demonstrates that the combination of two complementary ultrafast time-resolved methods, ultrafast x-ray, and electron diffraction will provide a panoramic picture of the transient structural changes in crystals.