飞秒脉冲激光序列在空气中的成丝传输

The filamentation of femtosecond laser pulses in air have attracted many attentions due to it's potential applications, such as lightning control, remote transportation of electromagnetic energy, laser modulated precipitation etc. However, the short lifetime of plasma channel produced by a single femtosecond laser pulse makes many applications difficult to be realized. This project is devoted to using femtosecond laser pulse sequence with a high repetition rate to produce long distance plasma channel with long lifetime. The physical properties and time evolution of plasma channel will be precisely measured. The physical mechanism of filamentation of femtosecond laser pulse sequence will be studied by both numerical simulations and experiments. The original results will be obtained due to the support of this project, which could contribute to improving the technologies based on laser filamentation.

飞秒激光在空气中的成丝传输过程一直受到极高的关注。主要原因是光丝的一些特殊性质能够衍生出许多潜在的实际应用，例如激光引雷，激光传导电磁能量，激光调节降水等。然而，单脉冲飞秒激光产生的电离通道寿命很短，制约了相关技术的实用化进程。本项目将对飞秒脉冲序列的产生及其在空气中的成丝传输过程开展深入的理论和实验研究。通过改善飞秒脉冲序列的参数产生长距离，长寿命的等离子体通道；对通道的物理性质和演化过程进行精确的实验诊断，揭示飞秒激光脉冲序列成丝的物理机制，取得原创性和突破性的进展，促进该领域的基础研究成果向实际应用的转化。

研制了用于放大脉冲序列的多通预防大器和主放大器。实验上研究了脉冲宽度仅7fs的少周期载波包络相位(CEP)稳定的激光脉冲在空气中成丝现象，首次观察到CEP对光丝电导率的调制作用，观察到光丝电导率随CEP以π为周期的变化。我们研究了TW级飞秒激光脉冲在自然大气中自由传输产生的长距离光丝的物理性质。结果显示飞秒激光脉冲自由传输产生的长距离光丝的电子密度在十的10^11/cm^3量级，与理论计算结果符合得较好，这是国际上首次获得的长距离光丝电子密度的定量实测数据。发明了一种新的测量飞秒激光脉冲在空气中产生的光丝的电子密度方法-电磁感应法, 该方法利用电磁感应线圈探测通电光丝周围的磁场变化来还原光丝的电子密度，并且同时获得了可靠的电子密度的时间演化过程。

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