Studies On Influence Of Laser Focus And Environment Parameters On Mechanical Effect Of Laser Plasma Shock Wave

The influence of the laser focus, environmental and target parameters on themechanical effect and acoustic wave effect of plasma shock wave produced during theinteraction between the laser and the target are investigated in this paper.The influence of defocus distance on the mechanical effect of the plasma shockwave induced by laser is analyzed. And it is presented that, the variance of laser powerintensity on the target surface is the main cause to the variance of impulse couplingcoefficient when the target is at negative defocus distance; the disturbance of the increaseof impulse coupling coefficient is lead by the reflection and collision by the plasmashock wave when the target is at positive defocus distance. The influence of incominglaser power intensity on the mechanical effect of the laser plasma shock wave is studied.The experimental results show that the influence of laser power intensity on the plasmashock wave is according to the principle of laser plasma shock wave when the incominglaser power intensity is much lower, the impulse coupling coefficient increases with theincoming laser power intensity firstly, then decreases sharply after the incoming laserpower intensity reaches a threshold vale and the laser plasma shielding effect occurs.There are different maximum impulse coupling coefficients for different incoming laserpower intensity when target is at different defocus distance.The influence of laser plasma shielding and rarefaction wave on the mechanicaleffect of the laser plasma shock wave is analyzed. It is concluded and validated relationsthat the impulse coupling coefficient change with the defocus distance at the differentincoming laser energy, and that the impulse coupling coefficient changes with the laserspot diameter at the different incoming laser power intensity. The influence of theenvironmental air pressure on the mechanical effect of the laser plasma shock wave isstudied. It was conclude that the influence of the air pressure on the mechanical effect ofthe plasma shock wave does much matter with the defocus distance of target.The influence of target materials, target areaand target structure on the mechanicaleffect of the plasma shock wave is analyzed. The effect of impulse coupling with targetmay increases effectively through choosing the axially and radially confined laser plasmashock wave reasonably; the target area should be chose reasonably because of thediffraction at target edge of laser plasma shock wave and the damp effect of air.The relationship between the laser plasma acoustic wave and laser plasma shock wave is also studied. A method to judge the mechanical effect of the laser plasma shockwave according to the character values of the laser plasma acoustic wave is got.The research results in this paper provide theoretical and experimental bases forutilizing the mechanical effect of the laser plasma shock wave optimistically. They arealso valuable reference for many fields such as laser propulsion, laser processing.