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. Non-linear regimes are often present just below the damage threshold thus requiring careful tuning of the laser parameters to avoid melting the materials. Detailed studies of the damage threshold of nanoscale materials are therefore needed. We present results on the damage threshold of gold (Au) nanowires when illuminated by intense femtosecond pulses. These nanowires were synthesized via the directed electrochemical nanowire assembly (DENA) process in two configurations: (1) free-standing Au nanowires on tungsten (W) electrodes and (2) Au nanowires attached to fused silica slides. In both cases the wires have a single-crystalline structure. For 790 nm laser pulses with durations of 108 fs and 32 fs at a repetition rate of 2 kHz, we find that the free-standing nanowires melt at intensities close to 3 TW/cm2 (194 mJ/cm2) and 7.5 TW/cm2 (144 mJ/cm2), respectively. The Au nanowires attached to silica slides melt at slightly higher intensities, just above 10 TW/cm2 (192 mJ/cm2) 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.