Simulations of femtosecond atmospheric filaments enhanced by dual pulse molecular alignment
Simulations of femtosecond atmospheric filaments enhanced by dual pulse molecular alignment
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DOI：
10.1103/physreva.85.043843
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发表时间：
2012-04
影响因子：
2.9
通讯作者：
J. Palastro;T. Antonsen;S. Varma;Yu-Hsin Chen;H. Milchberg
中科院分区：
文献类型：
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作者：
J. Palastro;T. Antonsen;S. Varma;Yu-Hsin Chen;H. Milchberg
激光脉冲在大气中传播时，由于空气分子的瞬时电子响应和延迟旋转响应引起的非线性折射率变化而自聚焦。如果脉冲功率足够，则聚焦脉冲强度可以超过电离阈值，从而导致等离子体灯丝。由于等离子体折射引起的散焦与由于瞬时和延迟响应引起的聚焦之间的平衡导致在高强度下的扩展传播。因为由第一脉冲（泵浦脉冲）引起的旋转响应在时间上是周期性的，由于分子的旋转本征频率的量子力学离散性，在重现周期处延迟的后续激光脉冲（探测脉冲）经历由先前脉冲留下的折射率修改的传播尾流。在这里，我们目前的传播模拟的基础上最近的实验[Varma等人。（未发表）]表明，轴向延伸的等离子体灯丝和探针脉冲整形所施加的分子对齐唤醒是敏感的探针延迟变化小至10 fs。
A laser pulse propagating through the atmosphere self-focuses due to the nonlinear index of refraction modifications from the instantaneous electronic and delayed rotational responses of the air molecules. If the pulse power is sufficient, the focused pulse intensity can surpass the ionization threshold, resulting in a plasma filament. The balance between defocusing due to plasma refraction and focusing due to the instantaneous and delayed responses results in extended propagation at high intensities. Because the rotational response induced by the first pulse (the pump pulse) is periodic in time, owing to quantum-mechanical discreteness of the rotational eigenfrequencies of the molecules, a subsequent laser pulse (the probe pulse), delayed at the recurrence period, experiences a propagating wake of index modification left behind by the previous pulse. Here, we present propagation simulations based on a recent experiment [Varma et al. (unpublished)] showing that axial extension of the plasma filament and probe pulse shaping imposed by the molecular alignment wake are sensitive to probe delay changes of as little as 10 fs.