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

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.

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