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The kinetic processes that affect the decay of (O2(1Δ) in the oxygeniodine transfer laser are discussed. The kinetics of O2* removal in the absence of iodine are now quite well established. A brief review of this topic is presented. 
 
When I2 is added to O2*, a distinction can be made between the behavior of O2* when both I2 and I are present, and when I2 is fully dissociated into atoms. In the latter case, energy pooling between O2(1Δ) and I* is the dominant process unless a strong I* quencher (e.g. H2O) is present. In the former case, the (O21Δ)-driven chain reaction mechanism for I2 dissociation is the dominant feature of the kinetics. A detailed description of each of these regimes is critical to the understanding of the oxygeniodine laser.

Behavior of singlet oxygen in the oxygen-iodine transfer laser

Molecular iodine dissociates in the presence of O(2)((1)Δ) and O(2)((1)Σ) molecules, but the mechanism of this process is not completely understood. In this paper, using flow tube experiments, we studied the initiation stage of iodine dissociation. Absolute spectral irradiance measurements were employed for measurements of concentrations of electronically excited particles. It was found that under the present experimental conditions initiation of iodine dissociation is mainly caused by reaction O(2)((1)Σ) + I(2) → O(2)((3)Σ) + 2I with a rate constant of (9.3 ± 2.0) × 10(-11) cm(3) s(-1). An appreciable role of the O(2)((1)Δ) molecule as the dissociation initiator has not been observed. It was observed that the growth rate of iodine atoms sharply accelerated when the concentration of I((2)P(1/2)) atoms approached 2 × 10(-4) of O(2)((1)Δ) concentration or when production rates of O(2)((1)Σ) molecules in reactions O(2)((1)Δ) + I((2)P(1/2)) and O(2)((1)Δ) + O(2)((1)Δ) became equal.

Dissociation of molecular iodine in a flow tube in the presence of O2(1Σ) molecules.

Optically pumped alkali vapor lasers are currently being developed in several laboratories. The objective is to construct high-powered lasers that also exhibit excellent beam quality. Considerable progress has been made, but there are technical challenges associated with the reactivity of the metal atoms. Rare gas atoms (Rg) excited to the np5(n+1)sP23 configuration are metastable and have spectral properties that are closely similar to those of the alkali metals. In principle, optically pumped lasers could be constructed using excitation of the np5(n+1)p←np5(n+1)s transitions. We have demonstrated this potential by observing gain and lasing for optically pumped Ar*, Kr* and Xe*. Three-level lasing schemes were used, with He or Ar as the collisional energy transfer agent that established the population inversion. These laser systems have the advantage of using inert reagents that are gases at room temperature.

Gain and Lasing of Optically Pumped Metastable Rare Gas Atoms

Rate constants for the removal of O2 b1Σg+ by collisions with species relevant to combustion, H2, CO, N2O, CH4 and C2H4 have been measured in the temperature range 297–800 K. O2(b1Σg+) was produced from ground-state molecular oxygen by photoexcitation pulses from a tunable dye laser, and the deactivation kinetics were followed by observing the temporal behavior of the b1Σg+–X3Σg– fluorescence. The removal rate constants for H2, CO, N2O, CH4, and C2H4 could be represented by the modified Arrhenius expressions kH2 = (1.44 ± 0.02) × 10–16T1.5 exp[(0 ± 10)/T], kCO = (6.9 ± 0.4) × 10–24T3 exp[(939 ± 33)/T], kN2O = (2.63 ± 0.14) × 10–18T1.5 exp[(590 ± 26)/T], kCH4 = (3.5 ± 0.2) × 10–17T1.5 exp[(−220 ± 24)/T], and kC2H4 = (2.34 ± 0.10) × 10–20T2.5 exp[(680 ± 16)/T] cm3 molecule–1 s–1, respectively. All of the rate constants measured at room temperature were found to be in good agreement with previously reported values, whereas the values at elevated temperatures up to 800 K were systematically measured for the f...

O2(b1Σg+) Removal by H2, CO, N2O, CH4, and C2H4 in the 300-800 K Temperature Range.

The kinetics of the processes occurring in an O2 – I2 – He – H2O gas flow in which photodissociation of molecular iodine at a wavelength close to 500 nm and excitation of atomic iodine on the 2P1/2 – 2P3/2 transition by narrow-band radiation near 1315 nm are implemented successively has been analysed. It is shown that implementation of these processes allows one to form an oxygen – iodine medium with a high degree of dissociation of molecular iodine and a relative content of singlet oxygen O2(a1Δ) exceeding 10%. Having formed a supersonic gas flow with a temperature ~100 K from this medium, one can reach a small-signal gain of about 10-2 cm-1 on the 2P1/2 – 2P3/2 transition in iodine atoms. The specific power per unit flow cross section in the oxygen – iodine laser with this active medium may reach ~100 W cm-2.

Kinetics of an oxygen – iodine active medium with iodine atoms optically pumped on the 2P1/2 – 2P3/2 transition

The results of our experimental study of the kinetics of formation of O2(1Σ) molecules in energy-exchange reactions O2(1Δ) + I(5
 p,2
 P
 1/2) and O2(a,1Δ) + O2(a,1Δ) are presented. The ratio of rate constants was obtained for these reactions (4800 ± 300). Setting the rate constant of the deactivation of O2(1Σ) molecules on CO2 molecules at 4.1 · 10–13 cm3/s, we evaluated the rate constants for these reactions at a temperature of approximately 330 K: (1.7 ± 0.2) · 10−13 and (3.6 ± 0.5) · 10−17 cm3/s, respectively.

Kinetics of formation of O2(1Σ) molecules in reactions involving excited O2(1Δ) oxygen molecules and I(2P1/2) iodine atoms

A novel optical pumping scheme considering a two-step irradiation by light at wavelengths near 500 nm and 1315 nm is proposed in this work. Radiation at 500 nm is used to dissociate about 1% of iodine molecules. The radiation at 1315 nm excites atomic iodine to the 2P1/2 state. Singlet oxygen molecules are produced via the energy exchange process I(2P1/2)+O2(X3Σ)→ I(2P3/2)+O2(a1Δ), while I(2P1/2)+O2(a1Δ) energy pooling produces b1Σ oxygen. I(2P3/2) and O2(1Σ) then accelerate the dissociation of I2. After gas dynamic cooling in supersonic nozzle, active medium may reach ~100 W cm–2 and small signal gain of ~0.01 cm-1.

Optically pumped oxygen-iodine laser

Dissociation of iodine molecules and singlet oxygen generation in O2 – I2 mixture induced by 1315-nm laser radiation

The experimental results on the dissociation of iodine molecules in the presence of single oxygen molecules under a widerange variation of the oxygen–iodine composition are presented. The rate constants are determined as 4.3 × 10-17 cm3 s-1 for the reaction O2(1Δ) + O2(1Δ) → O2(1Σ) + O2(3Σ) (reaction 1), 2.8 × 10-13 cm3 s-1 for the reaction O2(1Δ) + I(2P1/2) → O2(1Σ) + I(2P3/2) (4) and 8.3 × 10-11 cm3 s-1 for the reaction O2(1Σ) + I2 → O2(3Σ) + 2I (2). The analysis of the experimental results shows that for different compositions of the active medium of the oxygen–iodine laser the iodine dissociation occurs via the chain of reactions 1, 2, O2(1Δ) + I(2P3/2) → O2(3Σ) + I(2P1/2), 4 and in the cascade process I2 + I(2P1/2) → I2(u) + I(2P3/2), I2(u) + O2(1Δ) → 2I + O2(3Σ). For typical active medium compositions of the supersonic chemical oxygen–iodine laser, the contributions of each of the mechanisms to the dissociation are comparable. The experiments carried out did not reveal any contribution from the vibrationally excited oxygen molecules to the iodine dissociation. Thus, the performed experiments and the conclusions drawn from them completely confirm the mechanism of iodine dissociation, proposed earlier.

Experimental results on the dissociation of molecular iodine in the presence of singlet oxygen molecules

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