Extreme ultraviolet (EUV) light emission and ion emissions in the lateral direction generated by Nd:YAG irradiated droplet targets were studied experimentally under non-axisymmetric droplet irradiation. EUV energy monitors and ion electrostatic probes were positioned symmetrically at fixed positions around the plasma. Bulk ion kinetic energy $E_{kin}$ and bulk ion density $n_i$ were characterized for angles of $\gamma ={31}^{°}$ to $\gamma ={90}^{°}$ from the laser axis in a low-pressure nitrogen atmosphere of $1\times {10}^{-2}\mathrm{mbar}$. The EUV light emission reached a maximum level, with an increase of 5%, at $\gamma ={60}^{°}$ through a shift of the droplet by around 18% of the droplet diameter. The ion bulk kinetic energies at 31° and 75° also increased by 9% and 15%, respectively, with a small increase in ion density of around 3%. Intentional offset of the droplet target can, therefore, potentially result in higher EUV light output for non-axisymmetric mirror configurations, at the expense of a higher ion load but a decreased droplet fragment load. The ion kinetic energy showed a strongly anisotropic expansion behavior when offsetting the droplet relative to the laser focus, with kinetic energies increasing up to 60% in the lateral direction by offsetting the droplet by more than $0.5$ droplet diameters for a lateral range of 31°–90°. The ion density showed a more isotropic change with droplet offset, while maintaining a forward-peaked distribution.

中文翻译：

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非轴对称液滴辐照对激光等离子体光源离子和极紫外光发射的影响

在非轴对称液滴照射下，通过实验研究了 Nd:YAG 照射液滴目标产生的横向极紫外 (EUV) 光发射和离子发射。EUV 能量监视器和离子静电探针对称地放置在等离子体周围的固定位置。体离子动能${乙}_{克\mathrm{一世}n}$ 和体离子密度 $n_{\mathrm{一世}}$ 被表征为角度 $\gamma ={31}^{°}$ 至 $\gamma ={90}^{°}$ 从激光轴在低压氮气氛中 $1\times {10}^{-2}\mathrm{毫巴}$. EUV 光发射达到最高水平，增加了 5%，在$\gamma ={60}^{°}$通过将液滴移动约 18% 的液滴直径。31° 和 75° 处的离子体动能也分别增加了 9% 和 15%，离子密度略有增加，约为 3%。因此，液滴目标的有意偏移可能会导致非轴对称反射镜配置的 EUV 光输出更高，但代价是更高的离子负载但降低了液滴碎片负载。当相对于激光焦点偏移液滴时，离子动能表现出强烈的各向异性膨胀行为，通过将液滴偏移超过$0.5$横向范围为 31°–90° 的液滴直径。离子密度随着液滴偏移显示出更加各向同性的变化，同时保持前向峰值分布。