  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 scale
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 numerically simulated
using the two-temperature model (TTM) and the results agreed with experimental
observations. The ultrafast heating described by TTM was also discussed from an
electrical circuit perspective, which may provide new insights on the possible
connection between thermal and electrical processes. This study demonstrates
that the combination of two complimentary ultrafast time-resolved methods,
ultrafast x-ray and electron diffraction will provide a panoramic picture of
the transient atomic motions and structure in crystals.
