Research On Transient Evolution Characteristics Of Shock Wave Induced By Short-pulse Laser

When high power and narrow pulse laser acts on the surface of solid materials,it will produce high-pressure laser-induced shock wave.This kind of high-pressure shock wave driven by laser is widely used in laser shock strengthening,laser propulsion and other fields.How to achieve more accurate control of laser shock wave application and improve laser processing accuracy has become the focus of many scholars.However,at present,the understanding of laser-induced shock wave is not deep enough,and there are still some deficiencies in the generation and control of shock wave,which limit the deepening of the application level and the expansion of the application field of laser-induced shock wave.Only by mastering the mechanism and instantaneous evolution process of laser-induced shock wave,can we make better use of and control the effect of laser-induced shock wave,and realize the wide and deep application of laser-induced shock wave.Therefore,it is urgent to study the transient evolution characteristics of laser-induced shock wave.In order to solve this problem,theoretical and experimental studies on transient evolution characteristics of short pulse laser are carried out in this work.The results of this paper can play a certain role in the further application of laser-induced shock wave.Aiming at the shock wave induced by short pulse laser,the theoretical and numerical models are established,and the instantaneous evolution characteristics of shock wave under different laser energy and different spot size are calculated and analyzed.The results show that with the increase of laser energy,higher pressure is produced on the target surface,resulting in more severe impact process.Under the same laser intensity,with the increase of laser spot,the axial and radial development of shock wave presents equilibrium.With the increase of evolution time,the shape of shock wave front tends to be the same under the condition of larger and smaller spot.The numerical results provide some guidance for the design of the experimental device and the selection of experimental parameters.On the basis of theoretical research,based on the principle of high-speed shadow imaging,this paper establishes and improves the experimental system for the study of the instantaneous evolution characteristics of shock wave induced by short pulse laser,and carries out the experimental research on the evolution characteristics of shock wave induced by nanosecond pulse laser under different delay time and different time span.According to the instantaneous evolution radius and propagation velocity of shock wave,the evolution characteristics and laws are analyzed.With the increase of laser energy,the velocity of shock wave front accelerates,and the time of attenuation is advanced;under the same laser intensity,for the shock wave induced by small spot,the velocity of axial wave front is faster than that of radial wave in the initial stage,and the whole wave front is "conical".With the passage of time,the velocity of axial wave front decreases rapidly,and the shock wave front finally develops into hemispherical shape.When the laser irradiates on the uneven surface of the target,the shock wave has two or more wavefronts,and its envelope is random.With the increase of time,multiple wavefronts merge into one wavefront propagation.When there is gold in the environment,the shock wave can be divided into two or more wavefronts When it is a vapor sol,the laser is easy to break down and produce shock wave,and the double shock wave expansion and fusion phenomenon appears with the shock wave induced by the target itself.The location and intensity of the space shock wave have certain randomness.The results show that the evolution of shock wave induced by short pulse laser is in good agreement with the trend of theoretical calculation.The results of this study will have some beneficial effects on the development of laser shock strengthening,laser propulsion and other fields.