Researches On The Characteristics Of Shock Waves Of Laser-induced Water Plasma

The technology of pulsed laser to generate sound waves in the medium has broad application prospects in the emerging underwater communication field and Bottom detection field.Traditional electromagnetic wave communication is very suitable on land,but seawater has a very strong absorption capacity for electromagnetic waves,so it is impossible to use electromagnetic waves to communicate in seawater.The existence of a "blue-green window" in seawater allows lasers in this band to transmit a long distance in seawater,and combined with sound waves generated by light breakdown can achieve long-distance land-sea communication.Therefore,in this paper,the experimental device is used to photograph the underwater plasma expansion process using shadow imaging technology,and An experiment on the effects of experimental parameters on the acoustic wave signal of laser-induced water plasma,mainly including the following:(1)The optical shadow imaging method was used to study the laser-induced underwater plasma cavitation shock wave,and a clear image of the cavitation shock wave was obtained.It was clarified that the underwater plasma shock wave and sound wave were spherical waves.The expansion velocity of the plasma shock wave generated at 4mJ is 1799 m / s.(2)The laser plasma shock wave eventually decays into a sound wave during the expansion and transmission in water.Based on the research on the expansion process of laser-induced water plasma shock wave,through nanosecond pulsed laser energy,laser incident direction,laser wavelength,sound wave detection spatial position(horizontal and vertical),salt concentration of water,position of focus lens from water surface,the effects of laser-induced underwater plasma acoustic signals and their spectral characteristics have been studied and analyzed.The results show that with the continuous increase of the input laser energy,the intensity of the received laser acoustic wave signal increases continuously.With the increasing angle of the incident laser light,the fluorescence intensity of the underwater plasma continues to weaken,and the intensity of the acoustic signal of the laser underwater plasma also weakens.The intensity of the laser induced water plasma acoustic wave signal at 1064 nm is stronger than that of the laser underwater plasma acoustic wave signal at 532 nm.With the continuous increase of space distance,the intensity of the received laser acoustic wave signal decreases continuously.As the salt concentration in the solution increases,the intensity of the received laser acoustic signal increases.As the focus lens gets closer to the water surface,the fluorescence intensity of the underwater plasma continues to weaken,and the intensity of the laser underwater plasma acoustic wave signal also weakens.The intensity of the reflected signal from the aluminum target to the laser-induced acoustic wave is lower than that of the copper target.