使用一维辐射流体力学程序MULTI模拟了脉冲CO2激光烧蚀平面锡靶的过程, 研究了脉冲宽度、峰值功率密度、靶材初始密度对锡等离子体电子密度、电子温度的时空分布的影响, 并结合统计分析得到最有利于产生13.5 nm 极紫外光的激光脉冲宽度。模拟结果表明, 脉冲宽度为100~200 ns的长脉冲激光产生的等离子体有利于实现极紫外输出的最佳条件, 通过分析等离子体的电子密度、电子温度的分布对这一结论进行了解释。临界电子密度区域有效吸收了脉冲能量, 而低密度的羽辉对激光与极紫外辐射的吸收很少。采用长脉冲激光, 使得辐射极紫外等离子体持续时间更长, 是提高极紫外辐射效率的有效手段。同时模拟还发现, 靶材初始密度对等离子体参数的影响不大。

With the help of 1-D radiation hydrodynamic code MULTI, we simulated the ablation process of a pulsed CO2 laser irradiation on a tin planar target. We studied the influence of pulse duration, peak power intensity and initial target density on electron temperature and density distribution at different time. Also, the optimum pulse duration for 13.5 nm extreme-ultraviolet (EUV) emission was obtained by statistical analysis. It is found that long pulse duration , for example, 100-200 ns, is better for EUV emission. In this paper, the mechanism is discussed combining electron temperature and density distribution. Laser energy is effectively absorbed in the critical density area, while absorption of laser energy and EUV in the underdense corona can be negligible. Using a long CO2 laser pulse to prolong the EUV emission time can improve conversion efficiency effectively. Meanwhile, the initial target density has little influence on tin plasma parameters.