Optimization of /sub 2/ (/sup 1//spl Delta/) yields in pulsed RF flowing plasmas for chemical oxygen iodine lasers

Summary form only given. Chemical oxygen-iodine lasers (COILs) achieve oscillation on the ²P_1/2rarr²P_3/2 transition of atomic iodine at 1.315 mum by a series of excitation transfers from O₂(¹Delta). In conventional COILs, O₂(1Delta) is produced by liquid phase chemistry. In electrically excited COILs, (eCOILs) the O₂(¹Delta) is produced in a flowing plasma, typically He/O₂, at a few to 10s torr. One method to improve the efficiency of producing O₂(¹Delta) in eCOILS is by lowering the average value of electron temperature, T_e, using spiker-sustainer (S-S) excitation. In the S-S technique a high power pulse (spiker) is followed by a lower power period (sustainer). Excess ionization produced by the spiker enables the sustainer to operate with a lower T_e. Previous investigations have suggested that S-S techniques can significantly raise yields of O₂ (¹Delta). In this paper, we report on results from a 2-dimensional computational investigation of radio frequency excited flowing He/O₂ plasmas with emphasis on optimization of the S-S method. The model is a 2-dimensional plasma hydrodynamics simulation encompassing a solution of Navier Stokes equations for neutral flow dynamics. We found that the efficiency of S-S excitation, as measured by the yield of O₂(¹Delta), depends on a variety of parameters. These parameters include the details of the pulse shape, the carrier frequency, duty cycle (fraction of the S-S cycle for the spiker), S-S frequency (time between spiker pulses), spiker pulse shape and the ratio of spiker to sustainer voltage as well as on pressure. For a given T_e, the yield of O₂(¹Delta) largely depends on the energy deposition per O₂ molecule. As a consequence, the yield depends somewhat linearly on O_{2 mole fraction while the total O2(¹Delta) production is less sensitive to O2 mole fraction}