SEMICONDUCTOR-LASER ABSORPTION DIAGNOSTICS OF ATOMIC OXYGEN IN AN ATMOSPHERIC-PRESSURE PLASMA

Narrow-bandwidth semiconductor (GaAlAs) lasers have been used to recor d spectrally resolved atomic oxygen (7772 angstrom) and argon (8425 an gstrom) lineshapes, corresponding to the 3s5S2(0)-->3p5p3 and 4s3P1--> 4p3D2 transitions, in an atmospheric pressure, 1.4-kW, 27-MHz inductiv ely coupled argon-oxygen (12% O2/argon) plasma. Electron number densit y and kinetic temperature values were inferred from the Stark- and Dop pler-broadening components of the absorption lineshapes, respectively. The ionization temperature was calculated from the measured electron number density assuming ionization (Saha) equilibrium. Values of excit ed-state species number density and population temperature were determ ined from the frequency integrated absorption coefficient for each tra nsition. The difference between the ionization and population temperat ures reflects the presence of a suprathermal electron number density i n the flowfield. In addition, the excellent agreement between the kine tic and population temperatures suggests that the population in the ox ygen and argon lowest excited states may be described by a Boltzmann d istribution at the kinetic temperature. The methods presented extend e ffectively the range of semiconductor-laser diagnostics to mixed-gas p lasmas and flowfields containing atomic oxygen.