Thermal characteristics of double-layer thin film target ablated by femtosecond laser pulses

Thermal characteristics of tightly-contacted copper–gold double-layer thin film target under ablation of femtosecond laser pulses are investigated by using a two-temperature theoretical model. Numerical simulation shows that electron heat flux varies significantly on the boundary of copper–gold film with different maximal electron temperature of 1.15×10³ K at 5 ps after ablating laser pulse in gold and copper films, which can reach a balance around 12.6 ps and 8.2 ps for a single and double pulse ablation, respectively, and in the meantime, the lattice temperature difference crossing the gold–copper interface is only about 0.04×10³ K at the same time scale. It is also found that electron–lattice heat relaxation time increases linearly with laser fluence in both single and double pulse ablation, and a sudden change of the relaxation time appears after the laser energy density exceeds the ablation threshold.