Gd靶激光等离子体光源离带辐射及其等离子体演化的研究

Out-of-Band Radiation and Spatio-Temporal Characterization of Gd Target Laser Plasma Sources

利用脉冲宽度为10ns,输出波长为1 064nm的Nd∶YAG激光器作用金属Gd以及纳米粒子掺杂的低密度Gd玻璃等两种形式靶所产生等离子体光源的离带辐射进行了研究,发现等离子体所发出的连续辐射是离带辐射的主要成分,光谱分布与温度为5eV的普朗克曲线相匹配。此外,相对于金属Gd靶而言,采用纳米粒子掺杂的低密度Gd玻璃靶可大幅度降低等离子体光源的离带辐射。利用光谱法,对激光作用纳米粒子掺杂的低密度Gd玻璃靶所形成光源的等离子体羽的电子温度和电子密度进行了时空分辨研究。实验结果表明,在打靶结束125ns时,距靶面6mm位置处等离子体的电子温度约为4eV,电子密度约为1.2×1018 cm-3。同时发现在激光打靶结束后等离子体羽的电子温度和电子密度随延时的变化而呈指数下降,在120-250ns时间范围内,两者下降较快,之后其幅度下降缓慢。另一方面,当打靶脉冲结束约200ns时,在距离靶面1-10mm的空间内等离子体的电子温度及密度均经历先上升后下降的变化过程。在距靶材表面6mm位置处,电子温度和电子密度均达到最大值,电子温度约为2.6eV,电子密度为8.5×1017cm-3。

In this paper,an Nd∶YAG laser with 10 ns pulse width and output wavelength of 1 064 nm was employed to ablate Gd metal target and Gd-doped glass target for plasma generation.The out-of-band（OOB）radiation of extreme ultraviolet sources with the two target configurations was comparatively studied.It has been found that the continuous radiation emitted by the plasma is the main component of the out-of-band radiation.The spectral distribution of the continuum emission matches that of blackbody radiation with a temperature of about 5eV.And it is also found that the intensity of OOB radiation can be considerably decreased by using Gd-doped glass target.Optical Emission Spectroscopy（OES）has been used to analyze the temporal and spatial behaviors of electron temperature（Te）and density（Ne）of the Gd-doped glass target plasma,and experimental results show that temporal evolution of electron temperature and density of the plasma are found to be decayed exponentially with the increasing of delay time.At 125 ns after laser irradiation,electron temperature and density were 4eV and 1.2×1018 cm-3 respectively,and then decreased to 1.5eV and 8×1017 cm-3 with delaying time of 250 ns.On the other hand,spatial evolution of electron temperature and density show that both of them first increase and then decrease in the region of 1-10mm from the target surface.The electron temperature and electron density achieves the maximum of 2.6eV and 8.5×1017 cm-3,respectively,when the probe location away from the target surface 6mm.