真空环境下纳秒脉冲激光烧蚀典型材料的推进流场特性分析

Flow Field Characteristics of Nanosecond Pulsed Laser Ablation Propulsion with Typical Materials under Vacuum Conditions

关键词:  激光推进  烧蚀  流场  羽流特性  真空

Key words:  Laser propulsion  Ablation  Flow field  Plum characteristics  Vacuum1

摘要:

为研究纳秒脉冲激光烧蚀典型材料推进流场瞬态流动过程，采用流场显示阴影技术，实现纳秒级时间分辨率、毫米级空间分辨率的流场演化信息定量测量，解决激光烧蚀推进羽流的时间、空间高分辨率测量难题。对典型金属材料铝和典型聚合物材料的流场特性进行测量分析，并研究激光能量密度对羽流特性的影响。在典型时间尺度上，定性分析激光作用典型材料羽流特征与推进性能之间的关系。由于纳秒激光峰值功率高，当烧蚀金属材料Al时容易形成高温高压的等离子体羽流，等离子体喷射速度超过17km/s，等离子体羽流在百纳秒时间尺度离开靶面，对靶的力的耦合结束；当烧蚀聚合物PMMA和PVC材料时，PVC材料羽流喷射以等离子体和细小颗粒为主，喷射量较大且集中、方向性好，实验测量得到PVC工质真空羽流速度达到1500m/s，因此带来的反喷冲量以及推力都会较高。

Abstract:

To study the flow field characteristics of nanosecond pulsed laser ablation propulsion with typical materials，the display technology of shadowgraph is used to realize the quantitative measurement of the flow field information with the nanosecond time resolution and the millimeter level spatial resolution. This can solve the problem of the high time and space resolution measurement of the plume by laser ablation propulsion. The flow characteristics with typical metal materials Al and typical polymer materials were measured and analyzed，and the effects of laser energy density on plume characteristics were studied. On the typical time scale，the relationship between the plume characteristics and the propulsion performance is analyzed qualitatively. Because of the high peak power of the nanosecond laser，the plasma plume of high temperature and high pressure can be easily formed when the material is aluminum，the plasma expansion velocity exceeded 17km/s，the plume moves away from the target at the time scale of one hundred nanoseconds and the coupling process of the force to the target ends. When ablating polymer PVC and PMMA，the PVC plume jet are the plasma and small particles，the amount of injection is larger and concentrated，the direction is good. Experiments showed that its plume velocity exceeded 1500m/s in vacuum，so the reverse jet impulse and thrust will be higher.