Experimental Research On Femtosecond Laser Ablation Of Graphite

The extreme situation of substances can be achieved under irradiation of a high intensity femtosecond laser,which could be used on structure modification and material ablation.Since femtosecond laser develops rapidly,the researches of manufacturing various nano-structured by femtosecond laser interaction with the materials have been caused considerable concern in recent decades.The preparation of nano-periodic structures through the femtosecond laser interaction with graphite was reported in this paper,which provides experimental evidence for the eventual realization of controllable large-scale preparation of carbon nano-structures.The experiments of laser ablating the highly oriented pyrolytic graphite were carried out by using a femtosecond laser with pulse duration of 130fs,repeated frequency of 1KHz,output energy of 2-200μJ,and a central wavelength of 800nm.The effect of laser energy and pulse number on ablation depth and ablation area of the graphite was investigated.The calculated ablation threshold of graphite was 0.46J/cm~2.Moreover,the formation conditions of these nano-periodic structures were analyzed.Two different periodic surface nanostructures were observed after laser ablation with SEM.One of them was a structure including low-spatial-frequency structure LSFL with period of about 400nm.The other was a structure including a high-spatial-frequency HSFL with period of about 100nm.The formation conditions of the nanostructures were analyzed by changing the parameters such as laser energy and pulse number.The results indicate that:we can get two types of periodic surface structure by multi pulses ablation processing:HSFL and LSFL.An energy accumulation effect was existed in multi-pulses ablation processing was discovered.Depth and area of crater ablated by single laser pulse are direct proportion to logarithm pulse energy.We can not get surface periodic nano-structures after ablating by single laser pulse when the laser energy is lower then the damage threshold of graphite.However,for the same structures,the required pulse number of high-energy laser pulse is less than the low-energy.The configurations of our carbon nano-structures are similar to the typical periodic surface structures,though there are some differences in detail.The period of HSFL may depend on laser energy which would be approved in a future research.We believe that our discovery may play a very important role in the development of future large-scale carbon nano-structured direct-write technology.