飞秒强激光脉冲与团簇相互作用的实验研究
文献类型：学位论文
| 作者 | 李松 |
| 学位类别 | 硕士 |
| 答辩日期 | 2013 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 刘建胜 |
| 关键词 | 飞秒强激光脉冲 气体团簇 库仑爆炸 等离子体参数 离子能谱 团簇尺寸和尺寸分布 |
| 其他题名 | Experimental study of interactions of intense femtosecond laser pulses with clusters |
| 中文摘要 | 团簇，多达107个原子通过范德瓦尔斯相互作用结合在一起形成的集群，受到了人们的广泛关注。团簇在局部具有固体的密度，而宏观上却表现为气体的特性，这一特点使其得到了大量的研究。Becker等人于1956年首次发现了团簇的存在，Hagena等人则对其进行了大量的深入研究，并发现了其诸多应用，例如，X射线、高能电子和离子以及聚变中子的产生。特别是，飞秒强激光脉冲与含氘团簇喷流相互作用引发氘─氘核聚变实验的成功，为基于台式激光驱动含氘团簇库仑爆炸中子源的实现提供了一种可能的途径。本文围绕激光与团簇相互作用中激光等离子体参数的诊断与温度对团簇尺寸的影响等方面展开了相关的实验研究。研究的主要内容如下： 1． 设计了一种用于飞秒强激光与团簇相互作用的诊断激光等离子体参数的单光束飞秒探针方案。该方案采用光学Michelson干涉法测量电离后的电子密度，以此来间接测量等离子体通道内的高能离子密度，具有简捷性、易操作性、延时的准确性、高灵敏度和低成本等优点，能够准确的测量相互作用中的等离子体参数，为激光与团簇喷流相互作用的实验研究提供了有效的分析手段。 2． 通过降低异核甲烷（CH4）气体由锥形喷嘴向真空膨胀之前的滞止温度来增大团簇的平均尺寸。同时，我们进行了分析性的计算来估测平均团簇尺寸和尺寸分布。在室温（296 K）、60 bar气体背压和240 K、30bar气体背压的团簇源条件下所获得的甲烷团簇平均尺寸Nav分别为6230和6580。经验计算结果表明，240 K、30 bar条件下获得的甲烷团簇平均尺寸是相同气体背压、室温条件下获得的甲烷团簇平均尺寸的5倍。根据实验中测得的数据，我们得出一个有关甲烷团簇的Hagena参数与温度之间的强非线性关系： 。另外，通过调节激光与喷嘴开启之间的延时，我们分别分析了室温、60 bar，240 K、30 bar和190 K、30 bar下甲烷团簇库仑爆炸产生的质子平均动能，并由此研究了三种条件下甲烷团簇平均尺寸和尺寸分布宽度随延时的变化过程。结果再次证明，降低甲烷气体的滞止温度可以增大甲烷团簇的平均尺寸，进而提高质子的平均动能。因此，利用这种方法我们在相对较低的气体背压下制备尺寸更大的团簇。 3． 对强度为6×1017 W/cm2（55 fs，160 mJ，800 nm）的飞秒强激光脉冲与室温、30 bar气体背压下乙烷（C2H6）团簇喷流的相互作用进行了实验研究。实验结果表明了C2H6团簇库仑爆炸产生高能质子的过程，这些高能质子的平均动能和最大动能分别为12.2 keV和138.1 keV。通过延时优化能够获得半径约为5.4 nm的C2H6团簇，经验计算结果表明，这一尺寸是相同条件下制备的甲烷（CH4）团簇尺寸的1.9倍。理论分析表明，相同尺寸的C2H6团簇和CH4团簇库仑爆炸产生的质子和碳离子的平均动能近似相等。综合来看，可以推论：相比于氘代甲烷（CD4）团簇而言，氘代乙烷（C2D6）团簇作为激光驱动团簇核聚变反应的靶材更为理想。 |
| 英文摘要 | Cluster, van der Waals bonded agglomerations of up to 107 atoms, has received considerable attention, and has been studied for the merits of its internal solid density and gaseous characteristic in general. It has been found for the first time by Becker et al. in 1956, and intensively studied by Hagena, and been used for many applications, such as X-ray generation, production of energetic electrons and ions, and even nuclear fusion. Especially, the experimental realization of the deuterium-deuterium (D-D) nuclear fusion based on Coulomb explosions of deuterium containing clusters in gas jets driven by intense femtosecond laser pulses from table-top laser facilities with deuterium containing cluster jets would make possible the build-up of a neutron source. In this thesis, experimental investigations have been carried out on the diagnosis of the laser plasma parameters as well as the impact of temperature on the cluster size. The results are shown as follows: 1. A scenario of the single-beam femtosecond probe has been designed for diagnosing the laser plasma parameters on the interactions of intense femtosecond laser pulses with clusters. This scenario measures the density of electron ionized by using the optical Michelson interferometry, in order to indirectly measure the density of energetic ions in the plasma channel. It has many advantages, such as simpleness, ease of operating, accuracy of time delay, high sensitivity and low cost. Thus it can accurately measure the plasma parameters in the interaction of intense femtosecond laser pulses with clusters, providing an effective analytical means for the studies of laser-cluster interaction. 2. The average cluster size is increased by lowering the stagnation temperature of heteronuclear methane (CH4) gas before its expansion into vacuum through a conical nozzle. Analytical calculations were performed to evaluate the average cluster size and the size distribution. Two average sizes (Nav) of 6230 and 6580 of CH4 clusters were acquired with the source conditions of 30 bars at 240 K and 60 bars at 296 K, respectively. Empirical estimation suggests of a 5 times size increase at 240 K compared with that obtained at room temperature under 30 bars. A strong nonlinear relation of Hagena parameter for CH4 clusters was revealed from the measured data in the experiments. In addition, by adjusting the time delay between the laser pulse and opening of nozzle, the average kinetic energies of protons from the Coulomb explosion of CH4 clusters are analyzed under three different source conditions-60 bars at room temperature (296 K), 30 bars at 240 K and 30 bars at 190 K, respectively. Then the optimization of average sizes and distribution width σ with time delay are also researched under three different source conditions. The results repeatedly demonstrate that we can increase the average cluster size by lowering the stagnation temperature of the CH4 gas, increasing the average kinetic energies of protons. It can be inferred from the results that much larger average sized CH4 clusters can be made under lower backing pressure at low temperature. 3. An experimental investigation has been performed on the interaction of intense femtosecond laser pulses at the intensity of 6×1017 W/cm2 (55fs, 160mJ at 800 nm) with ethane (C2H6) cluster jets prepared under the backing pressure of 30 bars at room temperature (300K). The experiment shows the generation of energetic protons, whose average and maximum kinetic energies (KEs) are 12.2 keV and 138.1 keV respectively, by Coulomb explosion (CE) of C2H6 clusters. C2H6 clusters with about 5.4-nm radius were generated through the optimization of time delays. Empirical estimation suggests that the 5.4-nm radius of C2H6 clusters is 1.9 times larger than that of CH4 clusters prepared in the same conditions. Theoretical analysis has revealed that the final average KEs of protons and carbon ions generated from the CE of C2H6 clusters are near to ones from the CE of CH4 clusters for the same sized clusters. It may be inferred that the deuterated ethane (C2D6) clusters are more ideal than the deuterated methane (CD4) clusters for the laser-driven cluster nuclear fusion events. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/16742]  |
| 专题 | 上海光学精密机械研究所_学位论文 |
| 推荐引用方式 GB/T 7714 | 李松. 飞秒强激光脉冲与团簇相互作用的实验研究[D]. 中国科学院上海光学精密机械研究所. 2013. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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