超强短脉冲激光在不同密度分布等离子体中的自聚焦

讨论高斯型强激光束在具有初始柱对称密度分布的低密度冷等离子体中传播时，等离子体密度分布的不同对激光自聚焦的影响.推导出可以判断更有利于自聚焦发生的评价函数，这样通过比较不同密度分布的评价函数值就可以判断哪种密度分布更有利于自聚焦的发生.为了说明这种方法的有效性，对评价函数进行分析得出：在相同的激光场中等离子体柱的轴心密度给定时(以激光的光轴为轴)，离轴越远的地方密度越大及密度变化越陡，自聚焦越容易发生；相对论效应与有质动力共同作用比相对论的单独作用，自聚焦更容易发生.数值模拟证实了评价函数能准确的预测在不关键词：自聚焦相对论效应有质动力评价函数

Self-focusing of ultra-intense short laser pulses in plasmas with various density distributions

Effects of plasma density distributions on self-focusing of intense laser pulses propagating in an underdense cold plasma are investigated, where the laser intensity has a Gaussian distribution and the initial plasma density is cylindrical-symmetrically distributed. An evaluation function is derived to judge which type of plasma density distribution is more beneficial for the occurrence of self-focusing. Through analyzing and calculating the evaluation function, it is found that for a given laser field and with fixed initial plasma density along the central axis, which coincides with the axis of the laser beam, increasing plasma density with the distance from the axis favors self-focusing. Furthermore, the greater the density gradient, the more favorable. It is also found that the combined action of both relativistic and ponderomotive effects is of more advantage to self-focusing than that of relativistic effect alone. Numerical simulation confirms that the evaluation function is capable of accurately predicting the favorable role of plasma density distribution in producing laser self-focusing.