等离子体屏蔽和稀疏波对冲量耦合系数的影响

Influences of plasma shielding and rarefaction wave on impulse coupling coefficient

利用脉冲Nd:YAG激光作用在铝、铜靶上,研究了不同入射激光能量下冲量耦合系数和离焦量之间的关系,以及不同功率密度情况下冲量耦合系数和光斑直径的关系。实验表明铝靶在入射激光脉冲能量由75.8 mJ增加到382.3 mJ时,冲量耦合系数峰值对应的最佳离焦量由-10 mm处远离焦点向透镜方向移到-18 mm,而对应的激光功率密度仅由2.0×109W/cm2增加到3.9×109W/cm2;铜靶实验规律和铝靶类似。等离子体屏蔽的吸收作用导致了冲量耦合系数达到最大值后迅速降低。铝靶在入射激光功率密度由0.7×109W/cm2增大到1.0×1010W/cm2时,冲量耦合系数随光斑直径增大而增大,对应变化斜率由5.2×10-5N.s/(mm.J)增大到49.2×10-5N.s/(mm.J),表明了稀疏波对冲量耦合系数的削弱作用随入射激光功率密度增加而增加,随光斑直径增大而减小。

The relationship between the impulse coupling coefficient and the distance of the target from focus at different incident laser energy, and the relationship between impulse coupling coefficient and laser spot diameter at different incident laser intensity were studied by applying Nd.. YAG laser pulse on the AI（Cu） target. The experiments show that the target position corresponding to the peak impulse coupling coefficient moves towards to the lens with the increase of the laser energy, and the increase of the optimum intensity is small. These prove that the plasma shielding induces decreases impulse coupling coefficient to decrease after the peak value. On the other hand impulse coupling coefficient increases with the increase of the laser spot diameter in a linear way at the same incident laser intensity, and the slope is increased from 5.2×10^-5 N · s/（mm ·J） to 49.2×10^-5 N · s/（mm ·J） with the increase of the laser intensity from 0.7 GW/cm^2 to 10 GW/cm^2. This experimental result implies that the influence of the rarefaction wave on impulse coupling coefficient increases with the increase of the incident laser intensity, and decreases with the increase of the laser spot diameter.