Pulsed x-ray scattering is used to examine the lattice dynamics in gold nanoparticles in water following excitation with intense femtosecond laser pulses. At lower excitation power the initial lattice heating is followed by cooling on the nanosecond time scale. The decay can be described by solving the heat transfer equations including both the bulk conductivity in water and a finite thermal boundary resistance at the particle-water interface. The lattice expansion rises linearly with excitation power, up to an excitation power corresponding to a lattice temperature increase of 529 K. At higher temperatures the lattice shows a loss of long-range order due to pre-melting of the particles. At the bulk melting temperature, complete melting occurs within the first 100 ps after laser excitation.

• Received 23 June 2004

DOI:https://doi.org/10.1103/PhysRevB.70.195423