靶材厚度对透射式激光烧蚀性能的影响

Effects of Propellant Thickness on Laser Ablation Performance in Transmission Mode

关键词:  激光烧蚀  透射式  靶材厚度  羽流  靶坑  激光推进

Key words:  Laser ablation  Transmission mode  Propellant thickness  Plume  Ablation crater  Laser propulsion

摘要:

为从微观角度更加直观地研究靶材厚度对透射式激光烧蚀微推进性能的影响，采用刮涂法制作了6种不同厚度的聚叠氮缩水甘油醚/硝化棉(GAP/NC)共混聚合物掺杂红外吸收染料(IR)的烧蚀靶材，基于高速相机和高倍显微镜搭建了羽流观测系统和靶坑观测系统，研究了在纳秒脉冲激光辐照下，烧蚀厚度分别为33μm，53μm，78μm，104μm，125μm 和144μm的GAP/NC+IR靶材所产生的羽流流场随时间演变的微观过程和靶坑形貌的微观特征，从而建立了透射式激光烧蚀的微观特征与宏观推进性能的联系，进一步分析了其所表征的推进性能的优劣。结果表明:随着靶材厚度的增加，靶材的前沿喷射物初始速度由2100m/s单调降至1340m/s左右，预示着烧蚀比冲的减小；喷射物中大颗粒凝聚态物质增多，靶坑的体积增大，喷射质量增加，预示着烧蚀产生的冲量和冲量耦合系数的增大；喷射发散角减小，羽流方向性变好，但烧蚀过程对基底的冲击程度增强。

Abstract:

In order to study the effects of the propellant thickness on the performance of laser ablation from microscopic，6 kinds of ablation target，taking GAP/NC polymer blend doped with infrared absorbing dye(IR) as propellant，were made with different thickness by knife coating. The ablation ejections and shockwave generated by nanosecond pulse laser were recorded by high-speed camera and the ablation crater was observed by high-power microscope. With the help of the observing system constructed in this paper，the relationship between microscopic characteristics，including plume evolution process and ablation crater，and macro propulsion performance was established. The ablation performance of GAP/NC+IR propellant with the thickness of 33μm，53μm，78μm，104μm，125μm and 144μm were studied respectively. The experimental results show that when propellant thickness increases，the fraction of large condensed matter in ejections and the volume of ablation crater both grow，indicating larger mass of ejections and larger momentum and momentum coupling efficiency，while the ejection velocity of front particles slows down from 2100m/s to 1340m/s，resulting in the decrease of specific impulse. Moreover，thinner propellant can weaken the impact of ablation process on the substrate，while leading a larger divergence angle of ejections at the same time.