Owing to its distinctive photon energy range, vacuum ultraviolet (VUV) emission plays a key role in diverse photo-induced natural and technological processes. Atmospheric-pressure plasma produced VUV is central to resolve long-held issues in dynamics of natural (e.g., lightning) and laboratory (e.g., streamer) plasmas. Challenging the seemingly unavoidable vacuum systems used to prevent VUV emission quenching by ambient gases, here we report the first observation of vacuum-free generation of stable sub-110 nm VUV emission from atmospheric-pressure plasmas jetted into open air and atmospheric air plasma. Emission from atomic helium at 58.4 nm is observed from a nonequilibrium atmospheric pressure plasma jet (N-APPJ), jetted directly into ambient air. In a similar experiment, we also report VUV emission from excited nitrogen species in an atmospheric pressure discharge in ambient air. The photon emissions detected expand the window of photo-induced processes beyond ~10 eV commonly achievable by existing non-excimer VUV plasma sources, and enables direct photo-excitation and ionization of molecular species such as CO2 and many others. The thus-enabled direct photoionization of O2, O, and N species further justifies the role of direct photoionization in the dynamics of natural and laboratory atmospheric-pressure plasmas and informs the development of the relevant plasma photoionization models, which currently largely sidestep the sub-110 nm domain. These findings can make contribution to the complement of photoionization model of lightning, streamer, and other plasmas, open new avenues to quantify the yet elusive role of photoionization in the plasma dynamics.

中文翻译：

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大气等离子体 VUV 光子发射

由于其独特的光子能量范围，真空紫外 (VUV) 发射在各种光诱导的自然和技术过程中起着关键作用。大气压等离子体产生的 VUV 是解决自然（例如，闪电）和实验室（例如，流光）等离子体动力学中长期存在的问题的核心。挑战用于防止环境气体对 VUV 发射猝灭的看似不可避免的真空系统，在这里我们报告了第一次观察到从喷射到露天和大气等离子体中的大气压等离子体中无真空产生稳定的亚 110 nm VUV 发射。从非平衡大气压等离子体射流 (N-APPJ) 观察到 58.4 nm 处原子氦的发射，该射流直接喷射到环境空气中。在类似的实验中，我们还报告了环境空气中大气压力放电中激发态氮物质的 VUV 发射。检测到的光子发射将光致过程的窗口扩大到现有非准分子 VUV 等离子体源通常可实现的约 10 eV 以上，并使分子物种（如 CO2 和许多其他物质）的直接光激发和电离成为可能。因此，O2、O 和 N 物质的直接光电离进一步证明了直接光电离在自然和实验室大气压等离子体动力学中的作用，并为相关等离子体光电离模型的发展提供了信息，目前在很大程度上避开了子110 纳米域。这些发现有助于补充闪电、流光和其他等离子体的光电离模型，