Simulation And Experimental Study On Periodic Micro-nano Surface Of Silicon Induced By Femtosecond Laser

With the rapid development of micro-manufacture technology,the efficient fabrication of functional devices with specific surface micro-nano structures has gradually become a hot research topic.Due to the extremely high peak power and ultra-fast interaction time of femtosecond lasers,sub-micron periodic surface structures can be fabricated on any material surface by the one-step laser irradiation,which have extensive application prospects in the field of photonics,plasma,optoelectronics,thermal radiation sources and bio-optics.Therefore,it is of great scientific significance and application value to study the formation and evolution mechanism of the surface periodic structure induced by femtosecond laser.In order to reveal the internal mechanism of LIPSS formation and evolution,this paper studies the generation mechanism,spatial-temporal distribution and evolution mechanism of silicon surface free electrons under femtosecond laser irradiation from the perspective of laser and matter interaction.The motion rule of laser irradiated silicon surface plasmon and the influence of its incident laser energy distribution are obtained.Then the related ionization mechanism and electron-lattice relaxation process in the interaction between laser and matter are considered comprehensively.The effect of incident laser energy distribution on the ultrafast process of femtosecond laser irradiation of single crystal silicon was analyzed based on ionization rate equation,dual temperature model,Drude model and plasmon.A simulation model of LIPSS prepared by femtosecond laser irradiation of single crystal silicon was established according to the related theories of solid physics and quantum mechanics.The influence of transient thermal properties of the target during energy coupling,such as electroacoustic coupling and electron diffusion on the formation and evolution of LIPSS are studied by means of simulation.Simulation results show that the smaller the electron diffusion coefficient of the material and the stronger the electroacoustic coupling strength,the more favorable to obtain a periodic stripe structure on the surface of the material.In order to further compare the effects of electron diffusion and electroacoustic coupling on the formation process of LIPSS,the femtosecond laser was used to prepare the surface of materials with different properties(copper,sapphire).The influence of laser parameters on formation of periodic surface fringe microstructure was studied.The experimental results show that the LIPSS induced on the semiconductor and insulator materials is more obvious and has a greater depth than that on the metal target,due to the smaller electron diffusion coefficient and the stronger the electroacoustic coupling strength disclosed.This is in a good agreement with the simulation results which indicates a more favorable mechanism of the formation of periodic stripe structure on the surface of the material.This study is of great significance for further understanding the formation and evolution mechanism of LIPPS,and provides theoretical and experimental guidance for obtaining laser-induced high-quality LIPPS structures.