飞秒激光烧蚀高定向热解石墨的超快过程研究

脉冲激光烧蚀高定向热解石墨(HOPG)是制备富勒烯、碳纳米管等碳纳米材料的重要方法之一。研究和认识飞秒脉冲激光烧蚀高定向热解石墨的超快物理过程,可以为探索飞秒激光烧蚀制备各种碳纳米材料提供重要的实验和理论基础。利用抽运-探测技术记录了0.33～20J/cm2不同激光能流下50fs激光脉冲烧蚀高定向热解石墨在0～9ns时间窗口内的超快动态过程,并且比较分析了烧蚀高定向热解石墨和烧蚀铝靶的差别。实验发现,随着入射到高定向热解石墨表面的激光能流从20J/cm2下降到0.33J/cm2,光热机制导致的物质去除逐渐减少,光机械机制的应力释放导致的大颗粒物质喷射逐渐成为主要的物质去除过程。分析表明,靶材的吸收系数是导致高定向热解石墨和铝靶烧蚀动态过程不同的主要因素。

Investigation of the Ultrafast Process of Femtosecond Laser Ablation of Highly Oriented Pyrolytic Graphite

Pulsed laser ablation of highly oriented pyrolytic graphite (HOPG) is one of the most important methods for fabricating fullerene, carbon nanotube and other carbon nano-materials. Investigation of the ultrafast process of femtosecond laser ablation of HOPG can provide important insights for exploring the method of producing carbon nano-materials with femtosecond laser. Using the pump-probe technique, the ultrafast processes of 50 fs laser ablation of HOPG at different laser fluences from 0.33 J/cm2 to 20 J/cm2 are investigated within the time window of 0~9 ns after the laser pulse strikes the target. The differences between the ablation processes of HOPG and aluminum under the strike of laser pulses with the same parameters are studied. It is found that as the pump laser fluence changes from 20 J/cm2 to 0.33 J/cm2, the HOPG target material removed by the photothermal mechanism gradually decreases; however the ejected material composed of larger particles induced by the photomechanical mechanism gradually increases. It is also found that the absorption coefficient of the ablated target is the main factor that causes the differences between the ablation processes of HOPG and aluminum.