Sheng H, Kim K Y, Kumarappan V, Layer B D, Milchberg H M
Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742, USA.
Phys Rev E Stat Nonlin Soft Matter Phys. 2005 Sep;72(3 Pt 2):036411. doi: 10.1103/PhysRevE.72.036411. Epub 2005 Sep 21.
We demonstrate the efficient generation of plasma waveguides in elongated cluster gas jets using 100 ps axicon-generated Bessel beam pump pulses. The plasma waveguide space and time evolution is measured using picosecond interferometry. Small radius waveguides with central densities as low as approximately 10(18) cm(-3) can be generated with this technique. Despite the expected subpicosecond cluster disassembly time, we observe long pulse absorption efficiencies that can be more than a factor of 10 greater than in unclustered gas targets of the same volume average atomic density. The maximum long pulse absorption observed in cluster jets under our range of conditions was 35%. The explanation for the enhanced absorption is that in the far-leading edge of the laser pulse, the volume of heated clusters evolves to a locally uniform and cool plasma already near ionization saturation, which is then heated by the remainder of the pulse. From this perspective, the use of clustered gases is equivalent to a supercharged preionization scheme for long duration laser pulses.
我们展示了使用100皮秒轴棱锥产生的贝塞尔光束泵浦脉冲在细长团簇气体喷流中高效产生等离子体波导。利用皮秒干涉测量法测量了等离子体波导的空间和时间演化。用这种技术可以产生中心密度低至约10¹⁸厘米⁻³的小半径波导。尽管预期团簇解体时间为亚皮秒，但我们观察到长脉冲吸收效率比相同体积平均原子密度的非团簇气体靶高出10倍以上。在我们的条件范围内，团簇喷流中观察到的最大长脉冲吸收为35%。吸收增强的解释是，在激光脉冲的远前沿，加热团簇的体积演化为已经接近电离饱和的局部均匀且冷却的等离子体，然后被脉冲的其余部分加热。从这个角度来看，使用团簇气体相当于一种用于长持续时间激光脉冲的增压预电离方案。
