纳秒激光对含能聚合物固体薄膜的烧蚀特性研究

Experimental Research for Effects of Nanosecond Laser on GAP Film Ablation Characteristics

关键词:  纳秒激光  激光烧蚀  含能工质  羽流演化  靶坑  激光推进

Key words:  Nanosecond laser  Laser ablation  Exothermic propellant  Plume evolution  Crater  Laser propulsion

摘要:

含能聚合物是激光烧蚀微推进中一类重要的推进剂，聚叠氮缩水甘油醚(GAP)是其中的典型代表。为了研究含能聚合物固体薄膜在纳秒激光下的烧蚀特性，使用8ns脉宽的Nd:YaG激光器以反射式和透射式烧蚀GAP固体薄膜靶材，对羽流演化过程和烧蚀坑形态进行了研究。结果表明:反射式烧蚀的羽流中喷射产物以气态为主，固态碎片较少，受迫形成锥面喷射，羽流演化速度较快。透射式烧蚀喷射在约束作用下，有大量固态碎片以球面膨胀，约束在羽流演化的早期抑制了喷射速度，但会逐渐碎裂分解释放产物和能量，使喷射前沿再次加速，约束延长了烧蚀区在靶材滞留的时间，使透射式烧蚀的靶材内热传导效应更为显著。在此基础上，以不同激光能量密度透射式烧蚀靶材，研究透射式烧蚀能量沉积区与周围工质的侵蚀和约束关系。结果表明:激光能量密度越大，周围工质受到的侵蚀作用越强，烧蚀坑面积越大，能量沉积区受到的约束作用越弱，透射式烧蚀的羽流演化体现出部分反射式烧蚀的特征。

Abstract:

Glycidyl azide polymer(GAP) is an exemplary material for exothermic polymers，which are important propellants for micro laser ablation propulsion. To investigate the exothermic polymer solid film ablation characteristics under nano-second laser，an 8ns Nd:YaG laser was used to ablate GAP solid film in reflection mode and transmission mode，in which the plume flow and the ablation craters were researched. The results show that，in reflection mode，the ablated target mainly ejects gas，solid debris is rare and its ejection forms a conical surface，the evolution is quite fast. In transmission mode，the ejection is restrained by cover layer，enormous solid debris ejects and spherically expands，the cover layer would decompose and release gas product and energy during propagation，accelerating the jet. The ejection of energy deposition area is delayed so the heat conduction is relatively more severe in transmission mode. On this basis，the relationship between energy deposition area and surrounding area in transmission mode ablation is experimentally researched. The results show that，as the laser fluence increases，the encroachment on surrounding area increases，the crater area enlarge，the restrain on laser deposition area decreases，the plume evolution presents some charateristics of reflection mode.