掺杂吸收剂对激光烧蚀GAP推进性能的影响

Effects of Different Dopants on Laser Ablation Propulsion Performance of GAP

关键词:  激光烧蚀微推力器  纳米碳粉  红外染料  GAP  推进性能  真空

Key words:  Laser ablation micro-thruster  Nano carbon powder  Infrared dye  GAP  Propulsion performance  Vacuum

摘要:

对激光烧蚀微推力器而言，聚合物靶材的激光烧蚀推进性能至关重要。为了研究掺杂剂对靶材推进性能的影响，寻找优化靶材性能的方法，以含能聚合物聚叠氮缩水甘油醚(GAP)作为烧蚀靶材，以纳米碳粉和红外染料作为掺杂剂，采用高精度扭摆、能量计和高倍显微镜测量的方法，以冲量耦合系数、比冲和能量转化效率参数作为量化指标，改变聚合物的掺杂浓度、靶材厚度以及激光入射方式，对掺杂不同吸收剂后的GAP的推进性能进行了研究。结果表明:纳米碳粉以局部热区的形式加速聚合物的气化分解，推进性能受掺杂浓度的影响较小；掺杂纳米碳粉的GAP表现为面吸收特性，随着靶材厚度增加，喷射产物的气化程度降低，聚合物推进性能下降；较薄的掺杂纳米碳粉的GAP的等离子体阈值低，表现出高比冲和高能量转化效率，其中能量转化效率最优值接近300%，适合作为透射式激光烧蚀微推力器的烧蚀靶材。红外染料对1064nm波长的激光具有较好的吸收性能，掺杂红外染料使GAP对激光能量的吸收增强，化学能释放更充分；聚合物的推进性能对红外染料的掺杂浓度十分敏感，在掺杂浓度为5%时性能表现优秀；不同浓度红外染料掺杂下GAP的烧蚀深度不同，当靶材的厚度与烧蚀深度相近时，GAP的推进性能表现最好。

Abstract:

For laser ablation micro-thruster， the laser ablation propulsion performance of polymer target is of great importance. To explore the way to optimize polymer propulsion performance， the energetic polymer glycidyl azide polymer(GAP) was put as ablation target， doped with nano carbon powder and infrared dye， measured by high-precision torsion balance， energy meter and high-power microscope. Considering impulse coupling coefficient， specific impulse and ablation efficiency as quantitative indices， the effects of different dopants on the propulsion performance were studied by changing dopants concentration， material thickness and laser incident mode. The results show that nano carbon powders accelerate the gasification and decomposition of polymer in the form local hotspots， and the concentrations of carbon have little effect on the propulsion performance. The surface absorption characteristic of GAP after doped with nano carbon powders results in the decrease of gasification degree of plume and propulsion performance with the increase of thickness of GAP target. The thinner GAP target doped with nano carbon powders has lower plasma threshold， meanwhile， it has higher specific impulse and high ablation efficiency which is up to 300%. The infrared dye which has good absorption to the 1064nm wavelength laser promotes release of chemical energy by increasing the polymer absorptivity of laser and concentrations of IR-dye have a great effect on the propulsion performance. 5% concentrations IR-dye doping is appropriate. The IR-dye concentrations are crucial to absorption depth of GAP. When the thickness of target is close to absorption depth，the GAP has best propulsion performance. In conclusion，the thinner GAP doped with carbon powders is more suitable for laser ablation micro-thruster in transmission mode.