Transition regime in the ultrafast laser heating of solids

Based on the phenomenological theory of heat diffusion, we show that the generated peak temperature $T_{\text{max}}$ after absorption of a laser pulse strongly depends on the pulse duration. We identify three different heat conduction regimes which can be identified via a simple parameter that depends only on the pulse duration and on material constants. The phenomenological approach is supported by numerical simulations of heat diffusion and measurements of the thermal surface expansion after transient grating excitation with 1 ps and 10 ns optical pulses.