脉冲激光诱导铪等离子体超极紫外辐射特性研究

Study on Ultraviolet Radiation Characteristics of Pulse Laser-Induced Hafnium Plasma

实验上利用1.064μm波长的Nd∶YAG激光作用在真空腔内的高纯度固体铪(Hf)靶上产生等离子体,测量了不同功率密度下Hf等离子体在1.0~8.5 nm波长范围内的软X射线时间积分光谱。首先基于Cowan程序计算得到不可分辨跃迁峰(UTA)原子光谱数据,并将其展宽为Gaussian线型与实验光谱进行比较,两者吻合较好。随后基于碰撞辐射平衡模型(CRM)计算了电子温度在0~500 eV的Nd∶YAG激光Hf等离子体的离子丰度,结果表明,随着电子温度的增加,高价Hf离子的丰度增高,与实验光谱分析结果相吻合。实验与理论计算对比后发现:Hf XXI-Hf XXV离子的4f n-4f n-15g和Hf XXVII-Hf XXXV离子的4d n-4d n-15p不可分辨跃迁峰位于水窗波段。最后基于MED103模拟了实验条件下等离子体时空演化过程,获得了电子密度和电子温度时空分布,通过不同激光功率密度下电子温度和电子密度分布的分析对比,进一步验证了实验光谱和CRM计算的结果。

In the experiment of this work,high purity hafnium(Hf)sample are irradiated with the a 1.064μm Nd∶YAG pulse laser to generate plasmas in a vacuum chamber,and the soft X ray time integral spectra of Hf plasma in the wavelength range of 1.0~8.5 nm under different power densities are measured.First,the atomic spectrum data of unresolved transition arrays(UTA)atomic spectrum data is calculated based on Cowan program,and the data are broadened to Gaussian line shape,which is in good agreement with the experimental spectra.Then,the ion abundances of Hf plasma from Nd∶YAG laser with electron temperature ranging from 0 to 500 eV are calculated based on the collision radiation balance model(CRM).The results show that the abundance of high valence Hf ions increases with the increase of electron temperature,which is consistent with the experimental spectral analysis.Comparing experimental and theoretical calculations,it is found that the indistinguishable transition arrays of 4f n-4f n-15g of Hf XXI-Hf XXV and 4d n-4d n-15p of Hf XXVII-Hf XXXV are located in the water window band.Finally,based on MED103,the spatiotemporal evolution of the plasma under the experimental conditions is simulated,and the temporal and spatial distributions of electron density and electron temperature are obtained.Through the analysis and comparison of electron temperature and electron density distribution under different laser power density,the experimental spectrum and CRM calculations results are further verified.