Probing thermal dissipation dimensionality to laser ablation in the pulse duration range from 300 fs to 1 µs.

We propose a quantitative method to determine the thermal dissipation dimensionality to laser ablation. We derived an analytical expression for the melting condition due to a single pulse for arbitrary spot diameters and pulse durations, which explicitly contains the dimensionality of the thermal diffusion process. As a demonstration, we compared the analytical expression with multi-shot ablation thresholds measured over pulse durations of more than six orders of magnitude for copper. The result shows that the thermal dissipation processes dominate for pulse durations longer than 5 ps, while nonthermal processes begin to dominate for shorter pulse durations.