O2(1Δ) production and gain in plasma pumped oxygen-iodine lasers:: consequences of NO and NO2 additives

The 1.315 mu m [I(P-2(1/2)) -> I(P-2(3/2))] transition of atomic iodine in the chemical oxygen-iodine laser ( COIL) is pumped by sequential reactions of I-2 and I with O-2((1)Delta). In electrically pumped systems (eCOILs), electron impact excitation of O-2 produces the O-2((1)Delta) and also produces O atoms through dissociative excitation. The O atoms, through reactions with I-2, I(P-2(1/2)) and I(P-2(3/2)), lead to dissociation of I-2, quenching of the upper laser level and removal of the lower laser level. While dissociating I-2 is potentially beneficial, quenching of the upper laser level is detrimental and so management of the O atom density is necessary to maximize laser gain. In this regard, NO and NO2 additives have been used to manage the O atom density by cyclically reacting with O and I. In this paper, results from a computational investigation of eCOIL systems using plug flow and two-dimensional models are discussed where NO and NO2 additives are used. The system is a flowing plasma sustained in He/O-2/NO mixtures with downstream injection of NO2 followed by injection of I-2. We found that addition of NO and NO2 is effective in managing the density of O atoms and maximizing gain by minimizing quenching of the upper laser level. We found that by optimizing the additives, laser gain can be maximized even though O-2((1)Delta) densities may be lower due to the management of quenching and dissociation reactions.