Abstract: The specific impulse is the important evaluation indicator of the micro propulsion performance. Its accurate measurement can not only help to analyze the mechanism of laser ablation with matter，but also help the design of micro laser ablation thruster. In order to directly measure the specific impulse in laser ablation with matter，the method adopted here is that the impulse caused by pulsed laser ablation and the gravitation caused by the loss of the ablation mass applies act respectively on the balance in the same direction and in the opposite direction based on the model of torsion pendulum in vertical direction movement，so that the specific impulse can be obtained. The results show that，the maximum angle and the angle before it can be used to calculate the impulse and the mean value of the stable rotation angle can be used to calculate the loss weight. And the structure size of the balance is the key design element in the structure design.

Key words: Laser ablation；Micropropulsion；Specific impulse；Impulse measurement；Ablation mass measurement；Laser propulsion

摘要： 比冲是评价激光微推进性能的重要指标，比冲的精确测量有助于分析激光与工质的烧蚀耦合机理，也有助于激光烧蚀微推力器的设计。为了对激光烧蚀工质比冲参数进行直接测量，采用垂直运动的扭摆模型，使单脉冲激光烧蚀工质产生的冲量与烧蚀质量引起的重力同向作用和异向作用各一次的方式获得相应冲量和烧蚀重量，从而可以直接获得比冲。研究结果表明，根据每次扭摆转角最大峰值和达到最大峰值之前的转角测量值可得到冲量，根据每次扭摆转角的稳态转角均值可得到工质烧蚀重量，结构设计中，横梁的结构尺寸是扭摆的设计关键。提出一种可以同时测量出单脉冲激光烧蚀工质产生的冲量和相应烧蚀重量的方法。

关键词: 激光烧蚀；微推进；比冲；冲量测量；烧蚀质量测量；激光推进