Experimental Study On Femtosecond Shaped-pulse Ablation Of Cu And GDP Material

In recent years,more and more research interest has been put into the field of femtosecond laser ablation of materials,femtosecond laser micromachining has good prospects in industrial fabrication.Femtosecond lasers have short laser pulse,thus a small heat affected zone,shaped femtosecond laser pulse has even more advantage that the pulse shape can be changed to further control the ablation process,hence it will benefit micromachining even more.In this thesis,we use shaped femtosecond laser pulse to ablate single crystal copper and GDP film.The mechanism of single-crystal copper ablated by femtosecond shaped laser pulse and the formation of micro-holes in GDP films are analyzed.The research mainly includes the following aspects: In the experiment of single crystal copper ablated by femtosecond shaped-pules,investigation on how the numbers and interval of sub-pulses femtosecond laser pulses in the shaped pulse sequences with different energy fluxes influence the ablation depth,surface area,volume and crater morphology was performed.Results show that with the increase of sub-pulse interval,the ablation depth decreases gradually,nevertheless the surface area expands gradually.The gradient of depth is greater than that of surface area.Therefore,the ablation volume decreases with the increase of sub-pulse time interval.In this work,the plasma shielding mechanism,electron lattice coupling mechanism,electron heating mechanism have been carried on the analysis to the regularity of ablation depth,surface area and volume.The morphology of the ablation crater is further studied by combining the profile curve of the ablation crater and the analysis curve of the falling ash in the ablation crater.In the drilling experiments of femtosecond shaped pulses on GDP thin films,the effects of numbers and interval of sub-pulses in shaped-pulse sequence with various energy fluxes on the size and shape of ablation holes were investigated,the optimal pulse-shaping parameters for GDP drilling were obtained.Results show that the size,roundness and morphology of the ablation hole depend on the numbers and interval of sub-pulses in the shaped pulses with identical energy flux.In the drilling by transform limit pulses and three pulse sequences with small interval,three different energies were employed,the exit qualities of all three cases are decent and there are cracks around the exits.In conditions of an identical energy,the ablation hole drilled by the seven-pulse sequence presents better quality and roundness,the entrance diameters together with exit ones decline while the sub-pulse interval increases;when the number of sub-pulses is small,e.g.the three-pulse sequence,the diameter of the ablation hole has a strong dependence on the pulse energy,in which the higher energy leads to larger diameters of both entrance and exit,but the difference between diameters of the entrance and exit is rather small.When the number of sub-pulses is large,that is,the seven-pulse sequence,the diameters and difference between diameters of the front and back holes show weak response to the pulse energy.Because of the extremely short duration and the formidable peak power,femtosecond laser pulse fabricate little heat affected zone in ablation process,which makes femtosecond laser pulse a luminary in kinds of industrial micro-fabrication.Femtosecond shaped laser pulse possesses not only the advantage of femtosecond laser pulse but also the ability to control the ablation process with various pulse shapes.Thus,femtosecond laser pulse-shaping technique presents better effect in micro-fabrication.In this thesis,the single-crystal copper and GDP film were ablated by femtosecond shaped laser pulse.The mechanism of single-crystal copper ablated by femtosecond shaped laser pulse and the formation of micro-holes in GDP films are analyzed.The research mainly includes the following aspects:In the experiment of single crystal copper ablated by femtosecond shaped-pules,investigation on how the numbers and interval of sub-pulses femtosecond laser pulses in the shaped pulse sequences with different energy fluxes influence the ablation depth,surface area,volume and crater morphology was performed.Results show that with the increase of sub-pulse interval,the ablation depth decreases gradually,nevertheless the surface area expands gradually.The gradient of depth is greater than that of surface area.Therefore,the ablation volume decreases with the increase of sub-pulse time interval.In this work,the plasma shielding mechanism,electron lattice coupling mechanism,electron heating mechanism have been carried on the analysis to the regularity of ablation depth,surface area and volume.The morphology of the ablation crater is further studied by combining the profile curve of the ablation crater and the analysis curve of the falling ash in the ablation crater.In the drilling experiments of femtosecond shaped pulses on GDP thin films,the effects of numbers and interval of sub-pulses in shaped-pulse sequence with various energy fluxes on the size and shape of ablation holes were investigated,the optimal pulse-shaping parameters for GDP drilling were obtained.Results show that the size,roundness and morphology of the ablation hole depend on the numbers and interval of sub-pulses in the shaped pulses with identical energy flux.In the drilling by transform limit pulses and three pulse sequences with small interval,three different energies were employed,the exit qualities of all three cases are decent and there are cracks around the exits.In conditions of an identical energy,the ablation hole drilled by the seven-pulse sequence presents better quality and roundness,the entrance diameters together with exit ones decline while the sub-pulse interval increases;when the number of sub-pulses is small,e.g.the three-pulse sequence,the diameter of the ablation hole has a strong dependence on the pulse energy,in which the higher energy leads to larger diameters of both entrance and exit,but the difference between diameters of the entrance and exit is rather small.When the number of sub-pulses is large,that is,the seven-pulse sequence,the diameters and difference between diameters of the front and back holes show weak response to the pulse energy.