超短超强激光脉冲辐照超薄碳膜电离状态研究  

Ionization state of ultra-thin carbon film irradiated by ultra-short intense laser pulse

作　　者：白春江[1] 崔万照[1] 余金清[2,3] 

机构地区：[1]中国空间技术研究院西安分院空间微波技术重点实验室,西安710100 [2]帝国理工学院布莱克特实验室 [3]电子科技大学真空电子器件国家级重点实验室,成都610054

出　　处：《物理学报》2016年第11期72-79,共8页Acta Physica Sinica

基　　金：国家自然科学基金重点项目(批准号:U1537211)资助的课题~~

摘　　要：为了进一步理解极端条件下物质的电离特性,特别是超短超强激光脉冲辐照超薄靶时等离子体的形成与分布,本文以超薄碳膜为例,细致研究了超短超强激光脉冲辐照下原子的离化过程.分析和比较了强激光场直接作用电离和靶内静电场电离等两种场致电离形式,在碰撞电离可以忽略的情况下,发现更多的电离份额是来自靶内静电场的电离方式.研究了激光脉冲强度对电离的影响,发现激光脉冲强度越强,电离速度越快,产生的高价态离子所占比例也越高.当激光强度为1×10^(20)W/cm^2时,尽管该强度高于电离生成C^(+6)所需要的激光强度阈值,但该激光脉冲并不能将整个靶电离成C^(+6)离子,对此本文进行了详细的分析.在研究激光脉冲宽度的影响时,发现激光脉宽越小,电离速度越快,但越小的激光脉冲电离获得的高价态离子越少.Ion acceleration is of interest for applications in fast ignition,compact particle sources,medical science,and others.The formation of plasma is of fundamental importance for understanding ion acceleration driven by intense laser.In order to further understand the solid dense material ionization dynamics under ultra-strong field,we use two-dimensional particle-in-cell code to study the ionization process of ultra-thin carbon film,driven by ultra-short intense laser pulse,particularly to see the plasma generation and distribution during the interaction.When an ultra-intense short pulse laser irradiates a solid dense nm-thick film target,the collisional ionization can be ignored for such a thin film target.If the target thickness is larger than laser pulse skin depth,the formation of plasma is contributed from laser field direct ionization and the ionization of electrostatic field inside the target,both of which are discussed and compared by the simulation results in this work.The ionization directly stimulated by laser field happens only near the laser-target interaction surface.After the generation of plasma on the target surface,electrons are accelerated into the target because of laser ponderomotive force.A huge electrostatic field is formed inside the target as a result of hot electron transport in it,and ionizes the target far from the interaction surface.It is found that a bigger fraction of ionization is contributed from electrostatic field ionization inside the target.The effect of laser pulse intensity on ionization is studied in detail,in which the laser pulse intensity is changed from 1×10（18）W/cm2 to 1×1020W/cm2.Comparing the results obtained under different intensities,we can see that higher intensity results in higher ionization speed,and much higher-order ions can be generated.At an intensity of 1×10（20）W/cm2,although the intensity much higher than the threshold can generate C（＋6）,only a small part of ions can be ionized into C（＋6）.The reason is that the C（＋6）ions can be

关 键 词：等离子体形成 超薄碳膜 强激光场 场致电离 

分 类 号：O484[理学—固体物理]