Zhang Nan, Wu Zehua, Xu Kuanhong, Zhu Xiaonong
Institute of Modern Optics, Nankai University, Key Laboratory of Optical Information Science and Technology, Ministry of Education, Tianjin 300071, China.
Opt Express. 2012 Jan 30;20(3):2528-38. doi: 10.1364/OE.20.002528.
Dynamic characteristics of air plasma generated by focused double collinear femtosecond laser pulses with a time interval of 10 ns are experimentally investigated. The air plasma emission changes significantly when altering the energy ratio between the two laser pulses. Time-resolved shadowgraphic measurements reveal that a small volume of transient vacuum is formed inside the air shock wave produced by the first laser pulse, which causes the second laser pulse induced ionization zone to present as two separate sections in space. Also recorded is strong scattering of the second laser pulse by the ionized air just behind the ionization front of the first laser pulse produced shock wave. Due to the high intensity of the scattered light, coherent Thomson scattering enhanced by plasma instabilities is believed to be the main scattering mechanism in this case.
对时间间隔为10纳秒的聚焦双共线飞秒激光脉冲产生的空气等离子体的动态特性进行了实验研究。当改变两个激光脉冲之间的能量比时，空气等离子体发射会发生显著变化。时间分辨阴影图测量表明，在第一个激光脉冲产生的空气冲击波内部形成了小体积的瞬态真空，这使得第二个激光脉冲诱导的电离区在空间上呈现为两个分开的部分。还记录到，第二个激光脉冲被第一个激光脉冲产生的冲击波电离前沿后方的电离空气强烈散射。由于散射光强度高，等离子体不稳定性增强的相干汤姆逊散射被认为是这种情况下的主要散射机制。
