Study On The Control Of Surface Morphology Of Copper Ablation By Shaped Femtosecond Laser Focus

Femtosecond laser ablation has a broad application prospect in micro-nano machining.The extremely short femtosecond pulse width enables ultra-fine ablation and processing on the sample surface.Pulse shaping technology can control various properties of pulse,such as generating a specific pulse sequence and changing the pulse structure in time domain,so as to satisfy the research of many special physical processes.In this paper,on the basis of the Sine phase,the shaped pulses of the negative tertiary phase and the Alpha phase are also used to ablate polycrystalline Cu.Based on the previous study of the effect of energy flux on ablation morphology in our group,the effect of different focus positions on the ablation morphology of copper surface was innovatively studied from the perspective of focus position.We compared and analyzed the dependence between the ablation morphology obtained at different focal points under the three energies and the shaped change of the plastic pulse,and explained the underlying physical mechanism.Using the plastic three-pulse sequence produced by Sine phase,the morphology of the ablation crater and the diameter of the sample are studied with different parameters.It’s found that the dominant mechanism of ablation changes with the increase of energy flux,the dominant mechanism of plasma shielding effect under the lowest laser energy flux is the dominant mechanism for determining the ablation surface morphology,and gradually changes to the dominant mechanism of plasma defocusing effect under the condition of the highest laser energy flux.Moreover,the larger the energy flux,the greater the laser power density in the same phase condition,and the greater the internal and external diameter of the ablation region area of the sample surface.When using the negative cubic and Alpha phase reshaped pulse sequences to study the influence of different focus positions and different phase parameters on the ablation morphology,it was found that only the plasma defocusing effect dominated the surface morphology of the ablation crater under the highest laser energy flux condition.Under the condition of two low laser energy fluxes,the plasma defocusing effect has less effect on the internal diameter of the ablation crater,so that the ablative region cannot form a strong internal ring ablation structure or only formed a small internal ring structure.As the laser energy flux increases,the ablative surface morphology can also be optimized by adjusting the position of the laser focus and the sample surface and the parameters of the negative cubic phase and the Alpha phase.