Investigation on pulsed discharge mode in SF₆-C₂H₆ mixtures

The non-chain chemical HF(DF) laser is one of the most powerful electrically-driven lasers operating in mid-infrared, in which SF₆-C₂H₆ mixtures are often used as lasering media. Due to the electronegativity of SF₆, the discharge in SF₆-C₂H₆ presents a complicated discharge mode. To achieve reproducible pulsed laser output, pulsed discharge in SF₆-C₂H₆ mixtures is investigated for discharge mode using plane electrodes assisted by array pre-ionization spark pins in cathode surface. Firstly, two modes can be distinguished. One mode is called the selfsustained volume discharge (SSVD), which is characterized by spatial uniformity in the discharge gap and pulse to pulse repeatability. On the contrary, another mode includes random arc passages in the discharge gap and therefore cannot conduct lasering. By varying discharge conditions (gap voltage, gas pressure, etc) two discharge modes are observed. Secondly, the holding scope of the SSVD mode is analyzed for the optimal mixture ratio of 20:1, and the boundary tend of the holding scope of SSVD indicates there exists maximum gas pressure and maximum charging voltage for SSVD. Finally, the peak current of SSVD relates positively to charging voltage, while negatively to gas pressure, from which it is drawn that synchronous electron avalanches initiated by the sliding array overlap spatially into SSVD and thus SSVD is essentially an α ionization avalanche.