O 2 ( Δ 1 ) production in He∕O2 mixtures in flowing low pressure plasmas

Abstract

Chemical oxygen-iodine lasers (COIL) are attractive for diverse industrial applications because they are capable of high efficiency, high power operation, and because the 1.315μm wavelength can be transmitted through fiber optics and couples efficiently with most metals. Conventional COILs are pumped with O2(Δ1) that is generated by reaction of Cl2 in a basic H2O2 solution. Current trends in pumping COILs involve producing the O2(Δ1) in electric discharges, thereby circumventing the hazards, complexity, and weight associated with pumping and storing caustic liquids. In this work, we have investigated the scaling of O2(Δ1) yields with specific energy deposition in He∕O2 mixtures in flowing radio frequency (rf) discharges at pressures of a few to tens of Torr using a global plasma kinetics model. We found that O2(Δ1) yield increases nearly linearly with specific energy deposition in O2 molecules up to a few eV per molecule, with yields peaking around 30% by 5–8eV. Further increases in specific energy deposition serve only to increase O2 dissociation and gas heating, thereby reducing the O2(Δ1) yield. We also found that variations in peak yields at a given specific energy deposition are caused by secondary effects resulting from dilution, pressure, and power level. We show that these secondary effects alter the O2(Δ1) yield by shifting the O2(Σ1)∕O2(Δ1) ratio.