关键词: 激光推进, 击穿, 激波, 气蚀空穴, 纹影系统

Abstract: It is important to study on evolution of fluxfield to discover the mechanism of thrust formation in laser propulsion.
The process of shock wave spread in air and water is obtained by a set of schlieren systems and a high speed framing camera, during which the shock waves are generated by CO₂ laser-induced air breakdown with water as induction. It is found that cavitation appears two times. The first is caused by action of shock wave on water surface, which appears at initial time;the second is a low-pressure area because of action of evaporation induced by laser ablation on water surface,which appears at about 8 μs after the camera is activated. Experimental results show that after the breakdown,the evolution of fluxfield which transmits in incident direction of the laser in air is faster than that in opposite direction in water,with initial velocities of shock wave being about 6 km/s and 3.33 km/s respectively.Both velocities of shock wave follow exponential damping and attenuate to voice velocities at about 73.368 μs in air and 41.649 μs in water.This work is of promoting significance for laser propulsion with water as propellant.

Key words: laser propulsion, breakdown, shock waves, cavitations, schlieren system