Energy confinement and thermal boundary conductance effects on short-pulsed thermal ablation thresholds in thin films

For this paper, single-pulse ablation mechanisms of ultrafast laser pulses ($25\phantom{\rule{0.222222em}{0ex}}\mathrm{ps}$) were studied for thin gold films ($65\phantom{\rule{0.222222em}{0ex}}\mathrm{nm}$) on an array of substrates with varying physical properties. Using time-domain thermoreflectance, the interfacial properties of the thin-film systems are measured: in particular, the thermal boundary conductance. We find that an often used, and widely accepted relation describing threshold fluences of homogeneous bulk targets breaks down at the nanoscale. Rather than relying solely on the properties of the ablated Au film, the ablation threshold of these Au/substrate systems is found to be dependent on the measured thermal boundary conductance; we additionally find no discernible trend between the damage threshold and properties of the underlying substrate. These results are discussed in terms of diffusive thermal transport and the interfacial bond strength.