To probe the electron density distribution of the plasma,double-frequency grating shearing interferometry based on the soft X-ray laser technology is developed.The 13.9 nm Ni-like Ag soft X-ray laser is used as a probe to make attempt on the diagnosis of laser produced plasma from a planar gold wafer target.Clear interference fringes image is achieved,which fully demonstrates the practicability of this technology.However,there are some problems such as the unclear target surface in the image.Analysis indicates the main reasons of these problems and a reasonable solution is proposed to improve this technology.

针对高温稠密激光等离子体临界密度附近电子密度的诊断需求,发展了基于软X射线激光的软X射线双频光栅干涉诊断技术.利用波长13.9 nm的类镍银软X射线激光作为探针,掠入射式的双频光栅作为分光干涉元件,对激光辐照金平面靶产生的等离子体进行诊断尝试.实验获得了清晰的干涉条纹图像,充分表明该技术的实用性.但结果中存在靶面不清晰等问题,为此,提出了初步的解决方案.

It is important to diagnose electron density of a plasma irradiated by lasers for inertial confinement fusion, in high energy density physics and related fields, especially for measuring high-Z plasma near the interface. Use of soft X-ray laser as a probe is an important method in diagnosis of plasma electron density distribution. However, it is difficult to carry out the research in high-Z laser plasma, because of the problem of excessive plasma spontaneous radiation. In view of the characteristics of soft X-ray laser, several specific experimental techniques have been developed. By using these techniques, which can greatly suppress effects of spontaneous radiation, diagnosis of high-Z plasma with soft X-ray laser probe method becomes possible. As a typical example, an experiment of diagnosing gold plasma is performed and clear images are obtained, indicating that the techniques are effective and feasible.

The diagnoses of laser-produced plasma electron density have important significance for inertial confinement fusion, plasma physics, high energy density physics and other relevant fields, especially for measuring electron density distribution information of medium and high-Z material plasma near the critical density surface. With 13.9 nm Ni-like Ag X-ray laser serving as a probe, using double frequency grating shearing interference technique, the electron density distribution of plasma produced by laser irradiating a gold planar target is measured. Clear interference fringe image is obtained. Preliminary deduction of the fringe shows that the maximum density measured is about 1.4 times the critical density. It is found that there are some discrepancies between experimental results and simulation results, which provides a useful reference to the further optimization of the simulation program. The experimental results fully demonstrate that the soft X-ray double frequency grating shearing interference technique is practical to diagnose near-critical-density plasma of medium and high-Z materials, which will have a good application value.

为了研究类镍氪32.8 nm激光输出所需的等离子体状态，利用Cowan程序计算了类镍氪32.8 nm激光系统的有关原子参数。根据能级参数，建立并求解了准稳态近似下的有关能级速率方程，计算获得了激光上、下能级的相对粒子数密度和相对增益系数随电子温度和电子密度的变化规律，并分析了3d94p、3d94d和3d94f组态的能级对激光产生的影响。通过理论计算得到实现类镍氪32.8 nm激光输出所需的最佳等离子体状态。最佳电子温度约为75 eV，最佳电子密度约为1018 cm-3。计算结果为未来开展毛细管放电抽运类镍氪32.8 nm激光实验提供了理论依据。

为了提高毛细管放电类氖氩46.9 nm软X射线激光的强度，研究了主脉冲电流波形对等离子体Z箍缩过程、激光的产生时间及激光强度的影响。通过改变主开关导通电感，实现了对主脉冲电流上升沿的改变。随着电流上升沿的增加，激光尖峰幅值减小，激光产生时间增加。实验进一步研究了平均电流变化率对激光强度的影响:在毛细管内径3 mm、管内初始气压30 Pa的情况下，产生46.9 nm激光的最佳平均电流变化率约为7.0×1011 A/s。

介绍了在毛细管放电实验中采用预脉冲开关,成功地抑制了由于采用Blumlein传输线作为电流脉冲成形线时存在的前置固有脉冲对Z箍缩过程的破坏。同时成功地加载了预脉冲,建成了毛细管放电X光激光装置,实现了类氖氩46.9 nm软X光激光输出,准确地测量了激光波长,并对激光的一系列特性,包括激光的方向性、增益特性和束散角等进行了实验研究。这一装置提高了Marx发生器的使用效率,为进一步实现毛细管放电装置的小型化提供了一条有效的途径。此外还介绍了毛细管放电抽运机制可能的应用。

自软X光激光发现以来，实现低激发阈、台式软X光激光一直是一个十分重要的研究方向。利用毛细管放电激励产生软X光激光，是实现台式软X光激光的主要方案之一。实验采用20 cm长的毛细管，利用X射线二极管(XRD)探测了毛细管放电抽运软X光46.9 nm激光输出。研究表明，放电电极的材料并不是影响激光输出质量的决定性因素。但考虑到电极元素的飞溅，在长时间的实验研究中，选择钼电极更为有利。电极形状在放电过程中只影响预脉冲的导通情况，而对激光影响并不大。在更长毛细管的实验中，选择锥状端面的电极将有利于预脉冲的导通，以便获得激光输出。

在低气压(25 Pa)快电流前沿(27 ns)下，利用镀金X射线二极管(XRD)测量获得了毛细管放电软X射线激光尖峰输出。研究该软X射线激光输出特性，为其未来的应用打下基础。低气压和快前沿导致等离子体的快速箍缩，此时激光产生于背景光峰值附近，脉宽1.6 ns。实验测量了快速Z箍缩时激光的束散角和增益特性。采用小孔扫描法，测得激光束散角为5.3 mrad。通过改变增益介质长度的方法，测得介质的增益系数为0.45 cm-1，最大的增益长度积为8.28。此外利用单色仪在46.9 nm处测得了激光尖峰输出。

毛细管放电软X光激光方案是实现小型、台式、高效、经济适用的X光激光器的新途径。为获得稳定而较大的激光能量，对激光输出所依赖的众多参数进行优化是实验研究不可或缺的步骤。主开关结构直接决定着主脉冲电流的波形，继而影响激光输出。经过对三种主开关结构进行实验研究，结果表明：改进的并联金属棒支座圆环-小圆盘型主开关的导通电感比较合适，可产生较好的主脉冲电流。主脉冲电流和激光输出的平均值比改进前分别提高了4%和31%，而出光率比最初的金属圆筒支座圆环-大圆盘型主开关提高了60%。改进的主开关在获得稳定而较大输出能量的情况下仍然继承了金属圆筒支座圆环-小圆盘型主开关的高耐压性，同时保持了激光束较小的脉宽。