Study On Self-assembled Periodic Structure Of Semiconductor Surface And Its Characteristics Induced By Femtosecond Laser Double Pulse Sequence

Femtosecond laser induced self-assembly periodic structure on surface of various materials has been the focus of the optical field.The researchers mainly focused on two aspects: Firstly,the mechanism of femtosecond laser interaction with materials,Secondly,extending the application fields of femtosecond laser micromachining.The results show that the electron density excited by femtosecond laser irradiation has an important influence on LIPSS.The short pulse duration of femtosecond laser is shorter than that of the physical and chemical processes involved in the ablation process.Therefore,femtosecond laser double pulse irradiation technology not only provide a lot of possibilities for manipulating transient local electron dynamics,regulating the properties of transient local materials and controlling the corresponding phase transition mechanism but also give a new perspective to explore the formation mechanism of LIPSS.Our main work is that we can control the excited electron levels to change the LIPSS morphology and the property of LIPSS by an adjustable-timedelay femtosecond double pulse sequence.Experimental results in this paper are as follows:1?Low spatial frequency(LSFL)and high spatial frequency(HSFL)were obtained on Zn O surface irradiated by femtosecond double pulse sequence with different delay time.It is found that with increasing of the delay time,LSFL gradually transition to HSFL.The electron density on the Zn O surface excited by femtosecond laser at 800 and 400 nm were respectively calculated by using the electron rate equation.Finally,the results of structural transformation are explained by Sipe theory.2?Nano-structures with different morphologies could be obtained on ZnO surface irradiated by an adjustable-time-delay double pulse sequence with crossed polarization.By coating Au with magnetron sputtering and annealing treatments,Surfaces-enhanced-Raman-scattering substrate could be obtained.Under the given laser parameters,the Raman enhancement factor of the substrate is up to 1.2×10~4.3?Two types of LIPSS(LSFL and HSFL)could be obtained on 6H-Si C surface ablated by an adjustable-time-delay double pulse sequence with parallel polarization.It is also found that with increasing delay time,LSFL gradually changes to HSFL.We have performed the theoretical analysis to this phenomenon.The birefringence phenomenon was also observed in the ablation area of the 6H-Si C surface,and the birefringence signal vary with the changing of the delay time.We make a systematic analysis of the factors that cause the above phenomena.