Hierarchical Structures Fabricated By Ultra-fast Double-pulse Laser And Its Applications

Surface micro/nano structures have a great impact on performance of the materials.Different micro/nano structures can lead to different properties,such as superhydrophobicity,self-cleaning,low adhesion,high optical absorption,colorful surface and so on,with little or no effect on original substrates.These properties have broad application prospects in the aerospace,pipeline transportation,efficient use of solar energy,optical identification and many other fields.Femtosecond laser manufacturing has attracted extensive attention due to its high-precision,high-efficiency,non-contact,flexible and eco-friendly characteristics.Previous research demonstrated that the temporally-shaped femtosecond laser pulse trains can improve the processing efficiency and quality.Meanwhile,because the single pulse is split into two or more sub-pulses,the interaction between the laser and the material is changed during the processing,which will further induce the distinctive morphologies of the surfaces.In this paper,we study the interaction mechanism between femtosecond laser and solid surface based on the temporally-shaped femtosecond laser pulse trains.We use the temporally-shaped femtosecond laser pulse trains to study the ability of temporally-shaped femtosecond laser pulse trains to fabricate the micro/nano structures of semiconductor and metal surfaces.The main research contents and innovations are as follows:?1?We studied the silicon morphologies distinction between circularly polarized laser irradiation and linearly polarized laser irradiation.With circularly polarized laser irradiating in water,the uniformly silicon nanodots are obtained which is definitely different from the ripples that obtained with linearly polarized laser irradiation.In addition,we demonstrate its ability for surface enhanced Raman scattering.The silver nanoparticles are produced by femtosecond laser photoreduction,of which the diameter are 40-80 nm in the majority,accounting for 75.6% and the mean diameter is around 66 nm.The irradiated surfaces exhibit excellent SERS performances with a maximum enhancement factor up to 7.69×10⁷ when Rhodamine 6G is used as the probe molecule,which presents a huge potential for trace de-tection.?2?We present the novel micro/nano dual-scale structures formed on silicon surfaces by temporally-shaped femtosecond laser irradiation in water in one step.The dual-scale structures consist of microspikes??2?m width,?0.5?m height?covered with nanoripples??146 nm period?by linearly polarized laser irradiation.Meanwhile,similar microspikes covered with nanoparticles??90 nm diameter?were obtained by circularly polarized laser irradiation.The formation mechanism of the novel structures involves a combination of enhanced capillary waves induced by the enhanced laser energy depositing within silicon surfaces due to the second subpulse enhanced ionization and reheating effects and the subsequent laser energy shielding from generated bubbles.In addition,by irradiating silicon surfaces in AgNO₃ solutions,high SERS-active substrates that consist of novel dual-scale structures covered with nanoparticles were obtained?EF of ?10⁸?.?3?Femtosecond laser double-pulse train was used to process nickel surface in different atmospheres.The microspike-vertical stripe structure and the porous cage structure were obtained under the acetic acid.However,the nanograting-nanowire structure was obtained in air.