Study On Interaction Mechanism Between Laser-induced Cavitation Bubble And Metal Target Underwater

Interaction mechanism between laser and material in liquid is an important issue of fundamental theories in the filed of laser applications in liquid,such as laser lithotripsy,laser processing underwater,laser propulsion underwater.In this dissertation,we investigated the interaction mechanism between a metal target and a bubble laser-generated on the surface of the target by the means of theory,experiment and simulation.The influence of the bubble’s relative size,the bubble’s oscillation times,and the metal material on the coupling efficiency between the bubble energy and the target energy was analyzed.Research details are as follows:First,in order to investigate the interaction process between the bubble and the target,a simple experimental method based on laser beam transmission probe(LBTP)has been developed by using cylindrical lenses and apertures.The time dependence of the bubble’s radius and the target’s displacement can be obtained by only one measurement.The results showed that the bubble’s oscillation induced the target’s oscillation,and they were synchronic in time.The bubble’s final collapse effect contributed to the target’s final speed.Second,the developed experimental method and numerical simulation were applied to investigate the influence of bubble’s relati-ve size on the collapse features of the bubble induced on a finite metallic surface,and the influence of bubble’s relative size on the coupling efficiency between the bubble energy and the target energy.A correction factor based on the Raleigh collapse time formula is proposed to describe the collapse time of the bubble induced on a finite rigid boundary.The simulation results showed that the target momentum was largest when the bubble size was almost half of the target size under the same bubble energy,target mass and target volume.Third,optical beam deflection and high-speed photographic methods were employed to investigate the influence of bubble’s oscillation times on the coupling efficiency between the bubble energy and the target energy.The results showed that the bubble’s oscillation times decreased with the incident laser energy,resulting into the decrease of the target’s oscillation times.As a result,a preliminary theory was proposed to reveal the step increases of the kinetic energy transferred to the target during the process of increasing the incident laser energy.The results also inferred that decreasing the times of the bubble oscillation could increase the coupling efficiency between the bubble energy and the target energy.Finally,the influence of the target material on the coupling efficiency between the bubble energy and the target energy was investigated by theory,numerical simulation and experiment.The results showed that the laser absorptivity and the density of the target material are two important parameters impacting the target’s momentum under same incident laser energy and target size.The bubble size played a more important role when laser energy is very small,while the target density played a more important role when laser energy is large enough.The outcome of this dissertation will be helpful to deepen cognition about the interaction of laser and metal material.It is also relevant for laser machining,laser lithotripsy and laser propulsion in water environment.