离焦量对等离子体冲击波力学效应的影响

Influence of Defocusing Distance on Mechanical Effect of Plasma Shock Wave Induced by Laser

为研究激光等离子体冲击波力学效应受入射激光及环境因素的影响,利用波长1．06μm,脉冲能量320 mJ,脉宽10 ns的Nd;YAG激光作用在Al靶上,研究了冲量耦合系数（Cm）和离焦量（Z）之间的关系。实验发现在1．01×10^5 Pa情况下,初始时Cm随Z增大而增大,到Z=-12 mm附近达到最大值;而后Cm随Z增大而减小。在4000 Pa时,Cm随Z的变化关系与1．01×10^5 Pa时相似,但峰值位置后移。离焦量不同时,由于作用激光的功率密度不同而影响等离子体屏蔽效果;光斑大小不同将影响稀疏波作用,且离焦量正负不同时激光等离子体冲击波对靶的作用机制也明显不同,这些因素决定了离焦量对等离子体冲击波力学效应的影响。

Influence of incoming laser beam and environmental factor on mechanical effect of plasma shock wave wias studied. The experiment was performed by focusing output pulses of the Nd ： YAG laser at 1.06 μm wavelength with 10 ns pulse width and 320 mJ pulse energy on aluminum targets mounted on a ballistic pendulum. The impulse coupling coefficients Cm was determined as a function of target defocusing distance Z at 1.01×10^5 Pa. The impulse coupling coefficient increases slowly with the increasing of defocusing distance, and gets maximum quantity at defocusing distance about -12 mm. And then impulse coupling coefficient decreases sharply with the increasing of defocusing distance. The function at 4 ×10^3 Pa is similar to it at 1.01 ×10^5 Pa, except that the maximum at a larger defocusing distance. The intensity and the diameter of the laser spot are different at the different defocusing distance, so the rarefaction wave effect and the plasma shielding effect are different too. And the mechanical effects of plasma shock wave on target at different defocusing distance are also different. All these factors dominate the influence of defocusing distance on mechanical effect of plasma shock wave induced by laser.