O2(1Δ) production in flowing He/O2 plasmas. I. Axial transport and pulsed power formats

Chemical oxygen-iodine lasers (COILs) have promising applications due to their high efficiency and ease of scaling to multikilowatt powers. Recent research has focused on pumping the iodine with O2(1Δ) produced by electric discharges. In a previous work, a global model was used to develop reaction mechanisms and determine the specific energy deposition (eV/O2) required to obtain high O2(1Δ) yields for electric discharge COILs. Experiments have recently achieved positive laser gain and oscillation with these energy depositions and have highlighted the importance of axial expansion of the plasma in optimizing excitation of the O2(1Δ). In this work, the consequences of axial transport on O2(1Δ) yields have been computationally investigated in flowing He/O2 plasmas at a few Torrs using a one-dimensional plasma hydrodynamics and kinetics model. We show that the experimentally observed extension of the plasma glow upstream and downstream of the electrodes is due to electron diffusion and capacitive coupling of the radio-frequency power source. We also show that ≅50% higher O2(1Δ) yields can be achieved with a pulsed discharge combined with continuous-wave discharge