Study On The Optimal Control Of Surface Topography Ablated By The Shaped Femtosecond Pulse

Femtosecond laser ablation technology is widely used in the field of micromachining.The technology of shaping femtosecond pulse can precisely control the ablation according to change the shape or phase of a pulse.In this paper,we studied the optimal control of surface morphology of polycrystalline Cu which was ablated by the shaped femtosecond laser pulses.The details of our study are as follows:First,polycrystalline Cu were ablated by sine phase-shaped pulse sequences,and the changing laws of the surface morphology,inner and outer diameters of the ablated area were studied.The study found that the surface morphology is affected by the energy flux,the shape and the sub-pulse interval of the shaped pulse sequence.Under the two conditions of A=1.54 and A=3.05,the inner diameter of the ablation zone were decreasing with the increase of the sub-pulse interval under different energy flux conditions.Under the energy flux of 27.85 J/cm~2,the inner diameter showed a periodic oscillating with the increasing of the sub-pulse interval,we considered that the oscillating is resulted by the plasma shielding.The outer diameter was decreasing with the increasing of sub-pulse interval under the two lower energy flux,while it was increasing under the higher energy flux.This is because the plasma shielding effect is the positive mechanism for obtaining the outer diameter of ablation.The plasma shielding effect is more stronger under the higher energy flux,so the outer diameter has a slowly increasing.Then the effect of the surface morphology ablated by alpha phase and cubic phase shaped pulse sequences were studied.It was found that under the condition of the lowest energy flux,there was no strong ablation structure inside the ablation area,but there had strong ablation structure under the other two higher energy flux conditions.We calculated the percentage of effective ablation area under different shaped pulse sequences on all of energy flux conditions,and found that the effective ablation area was the maximum under the highest energy flux condition when ablated by the sine phase shaped pulse sequence A=1.54,and the ablation efficiency was highest,so it was the best condition to use to ablate in this study.