# Study on the Ablation Behavior of High-Intensity Lasers in Vacuum  
[PERSON]  
1 State Key Laboratory of Advanced Space Propulsion Technology and Application, Space Engineering University, Beijing 101416, China; [EMAIL_ADDRESS] (H.G. ); [EMAIL_ADDRESS] (B.D. ); [EMAIL_ADDRESS] (D.W.); [EMAIL_ADDRESS] (S.L. ); [EMAIL_ADDRESS] (Q.C. ); [EMAIL_ADDRESS] (T.Z)1 State Key Laboratory of Advanced Space Propulsion Technology and Application, Space Engineering University, Beijing 101416, China; [EMAIL_ADDRESS] (H.G. ); [EMAIL_ADDRESS] (B.D. ); [EMAIL_ADDRESS] (D.W.); [EMAIL_ADDRESS] (S.L. ); [EMAIL_ADDRESS] (Q.C. ); teng2020229@163.  
vacuum environment reduces plasma shielding effects, thus improving ablation efficiency. These relationships underscore the importance of carefully selecting laser parameters and environmental conditions to optimize micropore quality [12]. Recently, research has identified material evaporation and melt injection as the primary mechanisms responsible for the formation of ablative holes. When the laser irradiates the material surface, it first induces localized melting, followed by the rapid evaporation of the material. At the moment of evaporation, the recoil pressure generated by the evaporating material becomes sufficiently strong to expel the molten material from the ablation hole [13,14]. Based on the aforementioned mechanism, studies have shown that, in terms of machining accuracy (which refers to the degree to which the dimensions, shape, position, and other parameters of the fabricated workpiece conform to the design specifications, reflecting the precision and consistency of the machining process and serving as a key indicator of manufacturing quality), the drilling accuracy (which refers to the degree of conformity between the actual holes produced and the design specifications during the laser drilling process) of nanosecond lasers is lower than that of femtosecond and picosecond lasers [15]. However, from the perspective of machining efficiency (which refers to the speed and productivity of completing drilling operations per unit of time), nanosecond lasers exhibit higher efficiency due to their higher output power. Additionally, because of the longer duration of nanosecond laser pulses, more molten material is generated during the ablation process, and granular splashes can be observed around the ablation hole and heat-affected zone. At this point, some of the ablation products are deposited on the hole wall, significantly impacting the laser drilling process and the geometric shape [16,17]. The deposition of ablation products is closely related to environmental pressure [18, 19, 20]. Additionally, environmental pressure can also influence ablation efficiency and the diameter of the ablation hole [21]. [PERSON] et al. conducted a comparative study on the femtosecond laser drilling process of PMMA materials in vacuum and atmospheric environments. The study found that a vacuum environment is more conducive to plasma discharge, thus increasing ablation efficiency [22]. [PERSON] et al. investigated the effect of an environmental pressure range from 1 Pa to 105 Pa on femtosecond laser ablation of copper, and the results showed that environmental pressure can alter the ablation morphology by changing the focus position [21]. [PERSON] et al. studied the ablation behavior of alumina ceramics under different environmental pressures and found that the diameter of the ablation hole increases with the increase in environmental pressure. These findings indicate that a vacuum environment can significantly influence laser ablation behavior [23]. From the perspective of improving ablation efficiency, one of the mainstream approaches is the combined pulse drilling method. This method involves using a continuous laser to create a molten pool on the material surface, followed by the application of a short-pulse laser to ablate the molten pool area. Finally, the molten pool is expelled using the recoil pressure generated by the short-pulse laser from the plasma. [PERSON] et al.