Ablation mechanism of porous silicon nitride irradiated by continuous wave laser under tangential gas flow

Abstract In this study, the laser ablation mechanisms of porous silicon nitride under different gas environments and airflow velocities were compared. The high‐temperature pyrolysis characteristics of silicon nitride were integrated with thermal radiation principles to elucidate the “high‐temperature ring” recorded by thermal imaging cameras during ablation. According to the dynamic evolution of temperature distribution, the temperature inflection point corresponded to the ablation initiation time. The results revealed ablation initiation times of 2.0 and 0.7 s in air and nitrogen, respectively. A comparative analysis of the morphology and spectral characteristics of silicon nitride, subjected to short‐time laser irradiation in different gaseous environments, revealed the formation of an oxide layer, whose reflectivity was 20.6% higher than that of the original material, in air. This oxide layer formation resulted in the later initiation of ablation, the formation of smaller pit diameters, and in oxygen‐free ablation‐induced depths that exceeded those observed in air environments. Laser ablation experiments under high‐speed airflow revealed that unlike the porous ablation morphology observed in static air, higher oxygen‐content dendritic products formed under high‐speed airflow. As airflow velocity increased from 0 to 374 m/s, the ablation pit diameter decreased from 11.2 to 6.7 mm. This study provides a reference for evaluating laser damage characteristics and laser protection capabilities of porous silicon nitride. In addition, it reveals the severe high‐temperature ablation behavior of silicon nitride used as antenna radomes in high‐speed aircrafts.