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
²
P
_1/2
rarr
²
P
_3/2
transition of atomic iodine at 1.315 mum by a series of excitation transfers from O
₂
(
¹
Delta). In conventional COILs, O
₂
(1Delta) is produced by liquid phase chemistry. In electrically excited COILs, (eCOILs) the O
₂
(
¹
Delta) is produced in a flowing plasma, typically He/O
₂
, at a few to 10s torr. One method to improve the efficiency of producing O
₂
(
¹
Delta) 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 O
₂
(
¹
Delta). In this paper, we report on results from a 2-dimensional computational investigation of radio frequency excited flowing He/O
₂
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 O
₂
(
¹
Delta), 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 O
₂
(
¹
Delta) largely depends on the energy deposition per O
₂
molecule. As a consequence, the yield depends somewhat linearly on O
₂
mole fraction while the total O
₂
(
¹
Delta) production is less sensitive to O
₂
mole fraction