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.
Highlights
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
The transient structural changes of the 150 nm thick Al (111) single crystal after illumination with 400 nm femtosecond laser pulses were probed by 8.04 keV sub-picosecond x-ray pulses
The pump fluence used for the 150 nm single crystal sample is higher, the transient electric field strength may not be higher than those observed in aluminum plasmas generated by femtosecond laser excitation
Summary
Time-resolved electron diffraction can record higher-order Bragg diffractions and enable the observation of diffuse scatterings; the presence of tens of kV/m transient electric fields on the metallic or semiconductor sample may make the interpretation of electron diffraction data difficult.. X-ray pulses are insensitive to transient electric fields and their diffraction signals are solely related to lattice structure. The transient structural changes of aluminum crystals, illuminated with femtosecond laser pulses, were recorded in real time with the combination of x-ray and electron probes. In both experiments, the aluminum crystals are heated to a similar equilibrium temperature. The oscillation periods of crystals with different thicknesses are measured by both transmission and reflection diffractions, which agreed with the standing wave assumption
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
