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

Generation of singlet oxygen metastables, O2(a∆), 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 O2(a) to support I(P1/2 P3/2) lasing at high output power. This paper discusses the chemical kinetics of the generation of O2(a) and the excitation of I(P1/2) 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 O2 with Ar and/or He, leads to increased O2(a) production rates, resulting in O2(a) yields in the range 20-40%. At elevated power, the optimum O2(a) yield occurs at higher total flow rates, resulting in O2(a) flow rates as large as 1 mmole/s (~100 W of O2(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 O2(a), O2(b), O(P), I2, I(P3/2), I(P1/2), 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 O2(a) production at 1 kW have intriguing implications for the scaling of EOIL systems to high power.