No abstract

The dissociation of I2 molecules at the optical axis of a supersonic chemical oxygen-iodine laser (COIL) was studied via detailed measurements and three-dimensional computational fluid dynamics calculations. The measurements, briefly reported in a recent paper [Rybalkin et al., Appl. Phys. Lett. 89, 021115 (2006)] and reanalyzed in detail here, revealed that the number N of consumed O2(aΔg1) molecules per dissociated I2 molecule depends on the experimental conditions: it is 4.5±0.4 for typical conditions and I2 densities applied for optimal operation of the COIL but increases at lower I2 densities. Comparing the measurements and the calculations enabled critical examination of previously proposed dissociation mechanisms and suggestion of a mechanism consistent with the experimental and theoretical results obtained in a supersonic COIL for the gain, temperature, I2 dissociation fraction, and N at the optical axis. The suggested mechanism combines the recent scheme of Azyazov and Heaven [AIAA J. 44, 1593 (2006)], where I2(A′Π2u3), I2(AΠ1u3), and O2(aΔg1,v) are significant dissociation intermediates, with the “standard” chain branching mechanism of Heidner III et al. [J. Phys. Chem. 87, 2348 (1983)], involving I(P1∕22) and I2(XΣg+1,v).

The mechanism of I2 dissociation in supersonic chemical oxygen-iodine lasers (COILs) is studied applying kinetic-fluid dynamics modeling, where pathways involving the excited species I2(X Σ1g+,10≤v<25), I2(X Σ1g+,25≤v≤47), I2(A′ Π32u), I2(A Π31u), O2(X Σ3g−,v), O2(a Δ1g,v), O2(b Σ1g+,v), and I(P21/2) as intermediate reactants are included. The gist of the model is adding the first reactant and reducing the contribution of the second as compared to previous models. These changes, recently suggested by Azyazov, et al. [J. Chem. Phys. 130, 104306 (2009)], significantly improve the agreement with the measurements of the gain in a low pressure supersonic COIL for all I2 flow rates that have been tested in the experiments. In particular, the lack of agreement for high I2 flow rates, which was encountered in previous models, has been eliminated in the present model. It is suggested that future modeling of the COIL operation should take into account the proposed contribution of the above mentioned reactants.

A comprehensive three-dimensional computational fluid dynamics (3D CFD) modeling of flowing-gas Rb diode pumped alkali laser (DPAL) is carried out. The cases of H e / C H 4 and pure He buffer gases are investigated, and the output power and optical efficiency are calculated for various pump powers, mole fractions of methane, buffer gas pressures, and flow velocities. The model considers the processes of excitation of high levels of Rb, ionization, ion-electron recombination, and heating of electrons, which affect the diffusion coefficient of Rb ions. Two types of Rb DPAL were studied: a low-power laboratory-scale device with pump power of several tens of watts and a high-power multi-kilowatt laser. Efficient operation of the Rb laser using pure He as buffer gas can be achieved only in a large-scale laser with a pump beam cross-sectional area of several c m 2 . The calculated results for such a device were compared with those reported by Gavrielides et al. [J. Opt. Soc. Am. B 35, 2202 (2018)JOBPDE0740-322410.1364/JOSAB.35.002202], where a simplified three-level model based on the one-dimensional gas dynamics approach was applied.

The celebrated Rigrod model [J. Appl. Phys. 34, 2602 (1963)] has recently been shown to be inadequate for calculating the output power of gas-flow lasers when the quenching of excited species is slow and the optical extraction efficiency is high [Opt. Lett. 20, 1480 (1995)]. The previous analysis of two-level systems is presented here in detail and extended to include the chemical oxygen-iodine laser (COIL). For both two-level systems and COIL's, we obtained simple analytic formulas for the output power, which should be used instead of the Rigrod model. We present the formulas for Fabry-Perot, stable, and unstable resonators. Both the saturation parameter and the extraction efficiency differ from those appearing in the Rigrod model. The highest extraction efficiency is achievable for both stable and unstable resonators with uniform intensity distribution over the resonator cross section and is greater than that calculated by the Rigrod model. A rather surprising conclusion is that the extraction efficiency of unstable resonators can be increased substantially if one increases the length of the part of the mirrors lying downstream of the optical axis. The derived formulas are applied to describe published experimental results of supersonic COIL's. The dependence of the power on the threshold gain is evaluated and from this the plenum yield of singlet oxygen is estimated. The value of the yield is in better agreement with experimental measurements than that obtained by the Rigrod model.