"Temperature measurements in optically pumped nonequilibrium plasmas by laser induced fluorescence of vibrationally excited carbon monoxide"

Abstract

Summary form only given. It is well known that CO laser can be used to produce low translational temperature, non-equilibrium plasmas in high (/spl sim/1 bar) pressure mixtures of CO and common buffer species, such as nitrogen, argon, and/or helium. In this paper, we will present a new Laser Induced Fluorescence (LIF) thermometry technique, based on strong single photon allowed absorption from vibrationally excited (/spl nu/>7) levels of the ground electronic state of carbon monoxide. Optical pumping is a two-step process which combines resonant absorption of continuous wave CO laser radiation with anharmonic Vibration-Vibration energy exchange, producing non-equilibrium plasmas in the steady state. These plasmas are characterized by exceedingly high (and non-Boltzmann) vibrational mode disequilibrium, and low (/spl sim/400 K) to moderate (/spl sim/1000 K) rotational/translational. temperature. Electron production occurs by means of vibrational pooling collisions in which the sum of the vibrational energies of the colliding partners exceeds the threshold for ionization (/spl sim/33 quanta). In this highly vibrationally excited environment, strong single photon optical resonances exist to both the A and D' excited electronic states. In this paper we present proof-of-concept LIF temperature measurements in CO/Ar optically pumped mixtures. Rotational temperature determined by X/spl rarr/D' LIF is found to agree well (+/- 50 K) with temperature determined by FT-IR emission spectroscopy. Preliminary data employing X/spl rarr/A (4th positive system) LIF will also be presented as will modeling results illustrating the potential of two-dimensional (PLIF) temperature imaging.