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 × 10 3 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 0.04×10 3 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.