The electric oxygen-iodine laser:: Chemical kinetics of O2(a1Δ) production and I(2P1/2) excitation in microwave discharge systems

Generation of singlet oxygen metastables, O-2(a(1)Delta), in an electric discharge plasma offers the potential for development of compact electric oxygen-iodine laser (EOIL) systems using a recyclable, all-gas-phase medium. The primary technical challenge for this concept is to develop a high-power, scalable electric discharge configuration that can produce high yields and flow rates of O-2(a) to support I(P-2(1/2) -> P-2(3/2)) lasing at high output power. This paper discusses the chemical kinetics of the generation of O-2(a) and the excitation of O(P-2(1/2)) in discharge-flow reactors using microwave discharges at low power, 40-120 W, and moderate power, 1-2 kW. The relatively high E/N of the microwave discharge, coupled with the dilution of O-2 with Ar and/or He, leads to increased O-2(a) production rates, resulting in O-2(a) yields in the range 20-40%. At elevated power, the Optimum O-2(a) yield occurs at higher total flow rates, resulting in O-2(a) flow rates as large as 1 mmole/s (similar to 100 W of O-2(a) in the flow) for 1 kW discharge power. We perform the reacting flow measurements using a comprehensive suite of optical emission and absorption diagnostics to monitor the absolute concentrations of O-2(a), O-2(b), O(P-3), I-2, I(P-2(3/2)), I(P-2(1/2)), small-signal gain, and temperature. These measurements constrain the kinetics model of the system, and reveal the existence of new chemical loss mechanisms related to atomic oxygen. The results for O-2(a) production at 1 kW have intriguing implications for the scaling of EOIL systems to high power.