Effects of laser energy density on impulse coupling coefficient of laser ablation of water for propulsion

Time-resolved force sensing and intensified charge-coupled device (ICCD) imaging techniques were applied to the study of the effects of laser energy density on impulse coupling coefficient of laser ablation of water for propulsion. A Transversely Excited at Atmospheric pressure (TEA) CO₂ laser operated at 10.6 μm, 30 J pulse energy was used to ablate water contained in a quadrate quartz container. Net imparted impulse and coupling coefficients were derived from the force sensor data and relevant results were presented for various laser energy densities. ICCD imaging was used in conjunction with the dynamic force techniques to examine the dependencies on laser energy density. Results showed that the impulse coupling coefficient could reach a maximum value when laser energy density was about 10⁵ J/m², and it would increase before laser energy got to this point and would decrease after this point, and ICCD imaging supplied important phenomenon to explain this variation, which were water ablation before laser energy density got to 10⁵ J/m² and laser-induced air-breakdown with water as an induction when laser energy density was higher than 10⁵ J/m².