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.
- atmospheric pressure plasma
- vacuum ultraviolet (VUV) emission