  Ultrashort, intense light pulses permit the study of nanomaterials in the
optical non-linear regime, potentially leading to optoelectronics that operate
in the petahertz domain. These non-linear regimes are often present just below
the damage threshold thus requiring the careful tuning of laser parameters to
avoid the melting and disintegration of the materials. Detailed studies of the
damage threshold of nanoscale materials are therefore needed. We present
results on the damage threshold of Au nanowires when illuminated by intense
femtosecond pulses. These nanowires were synthesized with the directed
electrochemical nanowire assembly (DENA) process in two configurations: (1)
free-standing Au nanowires on W electrodes and (2) Au nanowires attached to
fused silica slides. In both cases the wires have a single-crystalline
structure. For laser pulses with durations of 108 fs and 32 fs at 790 nm at a
repetition rate of 2 kHz, we find that the free-standing nanowires melt at
intensities close to 3 TW/cm$^2$ and 7.5 TW/cm$^2$, respectively. The Au
nanowires attached to silica slides melt at slightly higher intensities, just
above 10 TW/cm$^2$ for 32 fs pulses. Our results can be explained with an
electron-phonon interaction model that describes the absorbed laser energy and
subsequent heat conduction across the wire.
