The development of a discharge oxygen iodine laser (DOIL) requires efficient production of singlet delta oxygen O2(α1 Δ) in electric discharge. It is important to understand the mechanisms of of O2α1 Δ) quenching in these devices. To gain understanding of this mechanisms quenching of O2(α]1 Δ)in O/O2/O3/CO2/He mixtures has been investigated. Oxygen atoms and singlet oxygen molecules were produced by the 248 nm laser photolysis of ozone. The kinetics of O2(α1 Δ) quenching were followed by observing the 1268 nm fluorescence of O2α1 Δ → X3 Σ transition. It is shown that vibrationally excited ozone O3(υ;) formed in the three-body recombination O + O2 + M →O3(υ) + M is an important O/O2/O3 quenching agent in O/O2/O3 systems. The process O3(υ ≥2) + O2(a1 Δ)→ 2O2 + O is the main O2(α1 Δ) deactivation channel in the post-discharge zone. If no measures are taken to decrease oxygen atom concentration, the contribution of this process into overall O2(α1Δ) removal is significant even in the discharge zone. It was found in experiment that addition of species that are good quenchers of O3(υ;) decrease O2(a1 Δ) deactivation rate in the O/O2/O3 mixtures.
A simplified two-level generation model predicts that power extraction from an cw oxygen-iodine laser (OIL) with stable resonator depends on three similarity criteria. Criterion τd is the ratio of the residence time of active medium in the resonator to the O2(1Δ) reduction time at the infinitely large intraresonator intensity. Criterion Π is small-signal gain to the threshold ratio. Criterion Λ is the relaxation to excitation rate ratio for the electronically excited iodine atoms I(2P1/2). Effective power extraction from a cw OIL is achieved when the values of the similarity criteria are located in the intervals: τd=5-8, Π=3-8 and Λ≤0.01.
Experiments with a flow cell apparatus imitating conditions of oxygen-iodine laser, equipped with a chemical jet singlet oxygen generator and an electric discharge iodine generator have been performed. I2 and CH3I in the flow of Ar were used as atomic iodine precursors.
The distributions of the electronically excited species along the flow were examined detecting their optical emissions. A straightforward comparison of two methods of oxygen-iodine medium production - conventional, by means of I2 dissociation in the singlet oxygen flow and with iodine atoms produced externally in the electric discharge - was performed.
It was found that stored electron energy lifetime had been about 30% longer, when iodine was produced from CH3I in the discharge, compared to the conventional I2 dissociation in the singlet oxygen flow. It was observed that maximums of the I(2P1/2) and I2(B) concentrations had shifted to the nozzle plane, when I2 in Ar carrier was subjected to the glow discharge, pointing to a nearly twofold increase in the I2 dissociation rate. Contrary to the known results for low iodine and singlet oxygen concentrations, squared dependence of the amplitude of the I2(B) luminescence maximum with I(2P1/2) concentration was observed in the dissociation region for both methods of iodine production.
The efficient power operation in a chemical oxygen-iodine laser for subsonic modes has been demonstrated. It is
shown that the substitution of the buffer gas N2 by CO2 does not cause any significant variation in the dependence of the
output power on the degree ofdilution ofthe active medium. The maximum power was 581 W for the flow rate of molecular
chlorine 22 mmole/s that corresponds to a chemical efficiency of &eegr;chem = 29%.
The mechanism by which I2(B) is excited in the chemical oxygen-iodine laser was studied by means of emission
spectroscopy. Using the intensity of the O2(b1&Sgr;,&ngr;'=0) → O2(X3&Sgr;,&ngr;''=0) band as a reference, I2(B) relative number densities were assessed by measuring the I2(B,&ngr;')→ I2(X,&ngr;") emission intensities. Vibrationally excited singlet
oxygen molecules O2(a1&Dgr;, &ngr;'=1) were detected using IR emission spectroscopy. The measured relative density of O2(a1&Dgr;,&ngr;'=1) for the conditions of a typical oxygen-iodine laser medium amounted to ~15% of the total O2 content. Mechanisms for I2(B) formation were proposed for both the I2 dissociation zone and the region downstream of the dissociation zone. Both pumping mechanisms involved electronically excited molecular iodine I2(A', A) as an intermediate. It has been suggested that, in the dissociation zone, the I2 A', and A states are populated in collisions with vibrationally excited singlet oxygen molecules O2(a1&Dgr;,&ngr;'). In the region downstream of the dissociation zone the intermediate states are populated by iodine atom recombination process. I2(B) is subsequently formed in collisions of I2(A',A) with singlet oxygen. We also conclude that I2(B) does not participate measurably in the I2 dissociation process and that energy transfer from O2(b1&Sgr;) does not excite I2(B) to a significant degree.