M. Nisoli et al., COHERENT ACOUSTIC-OSCILLATIONS IN METALLIC NANOPARTICLES GENERATED WITH FEMTOSECOND OPTICAL PULSES, Physical review. B, Condensed matter, 55(20), 1997, pp. 13424-13427
Nonthermal generation of coherent-acoustic phanons is observed in meta
llic nanoparticles of tin and gallium, which are solid and liquid, res
pectively, at room temperature, by applying femtosecond pump-and-probe
spectroscopy. Oscillations in the photo-induced differential reflecti
on are clearly detected in the picosecond time domain. The measured pe
riod increases approximately linearly with size over a wide range and
extracted sound velocities are consistent with those of bulk. Transiti
on to ballistic regime in carrier excitation is also discussed on the
basis of the disappearance of oscillations for particle sizes below ho
t-carrier mean free paths.