Optical damage threshold of Au nanowires in strong femtosecond laser fields

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.