Photoionization relevant extreme ultraviolet emission from developing low temperature plasmas in air

HBSummary form only given. Using a self-matched transmission line pulse generator, high voltage pulses with magnitude 10-25 kV and ~25 ns pulse width are produced to excite low temperature plasma (LTP) formation. In using a short pulse, plasma formation is initiated, but the external excitation is removed before spark formation is completed, thus enabling a study of the LTP during its developmental phase. Using imaging in the visible spectrum and electrical diagnostics, this has been confirmed.To observe the 120 nm - 150 nm range, discharges are guided along the surface of an MgF2 observation window. On the opposing side of the window an evacuated spectrograph with intensified CCD enables the observation of VUV emission. Since the LTP is intentionally limited to its developmental phase, very low total light emission is becomes a diagnostic issue. Hence, it was necessary to accumulate light over several 10s of formation events before discrete lines in the spectra became evident. With a sufficient number of pulses, an experimental spectrum is generated in the 120+ nm range which was found to be in excellent agreement with theoretical atomic spectra of nitrogen and oxygen, with an assumed electron temperature of 1.6 eV. Using a gas puff system combined with an otherwise evacuated spectrograph enables the observation of extreme UV (EUV) to VUV light (80nm - 120 nm). In the photoionization relevant region of the spectra (below 103 nm), the observable emission consists of atomic neutral and singly ionized oxygen as well as molecular nitrogen. Data suggests that additional ground state transitions are present, but unobservable due to self-absorption and low overall light intensity. Most notably, the presence of photoionization capable emission in developing low temperature plasmas in air is verified.