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，最早也是最令人印象深刻的壮举之一是，用透镜将激光脉冲聚焦到空气中，可以产生响亮而非常明亮的“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激发了许多理论和建模工作，并奠定了几项重要技术的基础，但对这一“雪崩”过程开始的详细实验研究从未进行过，主要是因为直到最近才有先进的基于激光的诊断工具可以进行这样的研究。击穿火花是由雪崩电离产生的，在雪崩电离中，单个种子电子在驱动激光场的作用下以指数方式倍增到强烈加热的云中。这个项目的实验将使用最新的马里兰大学开发的高分辨率诊断来研究雪崩的详细时间和空间发展，从单个电子开始，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超灵敏的痕量物种检测技术进行研究。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.