Avalanche Ionization Revisited: Ultrafast Plasma Dynamics and Applications

这个项目将研究雪崩电离现象。激光发明后不久，最早和最令人印象深刻的壮举之一是演示了用透镜将激光脉冲聚焦到空气中可以产生强烈而非常明亮的“击穿火花”，在这种火花中，分子被分解和电离，空气被强烈加热到接近太阳的温度。虽然这一结果在过去几十年里刺激了大量的理论和建模工作，并奠定了几项重要技术的基础，但对这种“雪崩”过程的开始进行了详细的实验研究--主要是因为直到最近才有基于激光的先进诊断工具能够进行这种研究。击穿火花是通过雪崩电离产生的，即一个种子电子被驱动的激光场指数级地倍增成强烈的热云。这项计划的实验将使用最新的大学。马里兰州大学开发了高分辨率诊断技术，以研究从单个电子开始的雪崩的详细时间和空间发展，以及快速增长的热等离子体云与周围气体的相互作用。此外，雪崩击穿将作为一种对痕量物种的超灵敏检测技术进行调查。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

This project will investigate the phenomenon of avalanche ionization. One of the earliest and most impressive feats of the laser, soon after it was invented, was the demonstration that focusing laser pulses with a lens into air could generate a loud and very bright ‘breakdown spark’, in which the molecules were broken up and ionized, with the air strongly heated to temperatures approaching that of the Sun. While this result has stimulated much theory and modeling work over the decades and underlies several important technologies, detailed experimental investigation of the onset of this "avalanche" process has never been done -- mainly because the advanced laser-based diagnostic tools that would enable such an investigation were not available until recently.Breakdown sparks proceed by avalanche ionization, in which a single seed electron is multiplied exponentially into a strongly heated cloud by a driving laser field. The experiments of this program will use the latest Univ. of Maryland-developed high resolution diagnostics to investigate the detailed time and space development of the avalanche proceeding from a single electron, and the interaction of the rapidly growing hot plasma cloud with the surrounding gas. In addition, avalanche breakdown will be investigated as an ultrasensitive detection technique for trace species.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.