Study on the surface morphology formation mechanism of femtosecond laser processing gold

•Obtain the surface morphology with simulation method.•The effect of gas cluster on the machining morphology is important.•More detailed micro pore surface morphology was observed.•Explain the mechanism of material removal from the perspective of phase transition. To find out the surface morphology formation mechanism when using femtosecond laser to drill holes on gold film. We used femtosecond laser with 800 nm wavelength and 1 kHz maximum frequency, gold film with a thickness of 200 μm on copper substrate to carry out the research. Based on two-temperature model, we studied the heat transferring and surface morphology formation mechanism of femtosecond laser processing gold with numerical simulation method. In experiment research, we used femtosecond laser to drill holes on gold film, the parameters of laser are the same as those of the simulation, then we used the AFM (Atomic Force Microscope) to observe and measure samples. We calculated the ablation threshold of 800 nm femtosecond laser on gold material according to the results of simulation, the value is 0.19 J/cm2. Considering micro forces on melted materials, we also got some micro surface morphologies’ pictures with the method of numerical simulation. We found some raisings around the edges of holes drilled by laser on gold, and their heights relative to surface are related to the energy of laser pulse. In experiment research, we have obtained some photos of surface morphologies, and holes’ depth, diameter and edge raisings’ height are consistent with the data in simulation. And we found a small concavity near the raising on surface, which can prove that the solid–liquid-solid phase transition exists in the processing. Through simulation experiments, we have discovered that gas–liquid interaction may be the mechanism behind the formation of rasing and concavity around the processing area. Further experimental verification will be conducted in future work. Through simulation experiments, we have discovered that gas–liquid interaction may be the mechanism behind the formation of rasing and concavity around the processing area. Further experimental verification will be conducted in future work.