Jarmila Kodymova

Experimental verification of the Einstein A-coefficient used for evaluation of O2(g) concentration in the chemical oxygen-iodine laser

This paper is a contribution to the current discussion on the Einstein coefficient for spontaneous emission (A-coefficient) of singlet delta oxygen, O2(g), that is often used for an evaluation of O2(g) concentration in a chemical oxygen-iodine laser (COIL). The published values of the A-coefficient vary in a wide range, corresponding to a radiative lifetime of O2(g), , from ~53 to ~151 min. This could make an evaluation of COIL operation questionable. In this paper, the Einstein A-coefficient is estimated, based on the comparison of O2(g) concentrations determined by two independent methods: electron paramagnetic resonance and emission spectroscopy. Within the accuracy of the experimental techniques used, the value of the A-coefficient resulting from our investigation is (2.24±0.40) × 10-4 s-1, corresponding to of ~74 min. This result is more consistent with the value of 2.58 × 10-4 s-1 of Badger et al [1] than with the value of 1.47 × 10-4 s-1 reported recently by Mlynczak and Nesbitt [2], who raised doubt about the Badger et al value.

Reactivity of fullerenes with chemically generated singlet oxygen

Non-reactivity of fullerene C60 in its ground state with electronically excited molecular oxygen, O2(1Δg), chemically generated externally, has been observed, which could contribute to a better understanding of the fullerene photooxidation mechanisms.

Chemical oxygen-iodine laser using a new method of atomic iodine generation

The chemical oxygen-iodine laser (COIL) with a new chemical method of atomic iodine production was investigated. In this system, iodine atoms are formed in the COIL cavity by the fast chemical reaction of hydrogen iodide with chlorine atoms that are also produced chemically. It was found that, in the absence of singlet oxygen, the ground state atomic iodine can be produced with a high yield (80%-100%). In gas containing singlet oxygen, a gain on 3-4 electronic transition in iodine atom was achieved (0.35% cm/sup -1/). Both the concentration of atomic iodine and the gain depend substantially on the ratio of reacting gases and the penetration of secondary gases into the primary gas flow. In laser experiments, effects of the flow rate of reacting gases and their penetration on the laser output power were found. The output power of 310 W was attained at chlorine flow rate of 27 mmol/spl middot/s/sup -1/ corresponding to chemical efficiency of 12.7%. This was the first time the gain and laser output power were achieved in the COIL with atomic iodine generated by the proposed method.

Chemical generation of atomic iodine for chemical oxygen–iodine laser. I. Modelling of reaction systems

Abstract The mathematical modelling of reaction systems for chemical generation of atomic iodine is presented. This process is aimed to be applied in the chemical oxygen–iodine laser (COIL), where it can save a substantial part of energy of singlet oxygen and so increase the laser output power. In the suggested method, gaseous reactants for I atoms generation are admixed into the COIL primary gas flow containing singlet oxygen. Two reaction systems were proposed, based on the reaction of hydrogen iodide with chemically generated atomic fluorine or chlorine. It was found that the reaction path via Cl atoms better matches the experimental conditions of COIL with a yield of atomic iodine of up to 67%. As a result of modelling, a suitable reaction system and design of experimental arrangement for the effective production of atomic iodine in laser conditions were found.

Experimental study of gain and output coupling characteristics of a CW chemical oxygen-iodine laser

Gain and output coupling characteristics of the CW chemical oxygen-iodine laser (COIL) are determined experimentally by means of varying the output coupling method. Under the conditions that the Cl/sub 2/ flow rate is 11.8 mmol/s, the I/sub 2/ molar flow rate is from 20 to 50 mu mol/s, and the duct pressure is 200 Pa, the following were obtained from the experimental data: maximum values of output power of 58 W, and optimal output coupling factor of 1.50%, a resonator efficiency of 4.8%, an unsaturated small-signal gain of 1.55*10/sup -3/ cm/sup -1/, a threshold small-signal gain of 1.31*10/sup -3/ cm/sup -1/, a saturation intensity of 1150 W/cm/sup 2/, intraresonator losses of 9%, and an atomic iodine concentration of 2.85*10/sup 14/ cm/sup -3/. A comparison of these results to the published data of other COIL systems is presented. >

Production of iodine atoms by RF discharge decomposition of CF3I

Generation of atomic iodine by dissociation of CF3I in a RF discharge was studied experimentally in a configuration ready for direct use of the method in an oxygen?iodine laser. The discharge was ignited between coaxial electrodes with a radial distance of 3.5?mm in a flowing mixture of 0.1?0.9?mmol?s?1 of CF3I and 0.5?6?mmol?s?1 of buffer gas (Ar, He) at a pressure of 2?3?kPa. The discharge stability was improved by different approaches so that the discharge could be operated up to a RF source limit of 500?W without sparking. The gas leaving the discharge was injected into the subsonic or supersonic flow of N2 and the concentration of generated atomic iodine and gas temperature were measured downstream of the injection. An inhomogeneous distribution of the produced iodine atoms among the injector exit holes was observed, which was attributed to a different gas residence time corresponding to each hole. The dissociation fraction was better with pure argon as a diluting gas than in the mixture of Ar?He, although the variation in the Ar flow rate had no significant effect on CF3I dissociation. The dissociation fraction calculated from the atomic iodine concentration measured several centimetres downstream of the injection was in the range 7?30% when the absorbed electric energy ranged from 200 to 4000?J per 1?mmol of CF3I. The corresponding values of the fraction of power spent on the dissociation decreased from 8% to 2% and the energy cost for one iodine atom increased from 30 to 130?eV. Due to a possible high rate of the atomic iodine loss by recombination after leaving the discharge, these values were considered as lower limits of those achieved in the discharge.

Chemical generation of atomic iodine for the chemical oxygen-iodine laser. II. Experimental results

Abstract A new method for the chemical generation of atomic iodine intended for use in a chemical oxygen–iodine laser (COIL) was investigated experimentally. The method is based on the fast reaction of hydrogen iodide with chemically produced chlorine atoms. Effects of the initial ratio of reactants and their mixing in a flow of nitrogen were investigated experimentally and interpreted by means of a computational model for the reaction system. The yield of iodine atoms in the nitrogen flow reached 70–100% under optimum experimental conditions. Gain was observed in preliminary experiments on the chemical generation of atomic iodine in a flow of singlet oxygen.

Performance Characteristics of Jet-type Generator of Singlet Oxygen for Supersonic Chemical Oxygen-Iodine Laser*1

A jet-type singlet oxygen generator based on a gas-liquid chemical reaction yielding singlet oxygen, O2(1Δ g), for pumping the supersonic chemical oxygen-iodine laser was investigated. In addition to O2(1Δ g) and residual chlorine concentrations, a content of water formed during O2(1Δ g) generation was estimated (because of its detrimental effect on lasing) in gas flowing from the generator to the laser active region. The experimental conditions were determined under which an effect of liquid droplets escaping from the generator was negligible, and accordingly, a content of water vapour was suppressed to a value corresponding to the saturated water vapour pressure. It was also proved that a reduction in the relative water content, and a consequent increase in the laser output power, could be achieved by increasing peroxide and hydroxide concentration in the generator liquid, and by decreasing a liquid temperature and a total pressure in the generator.

Contribution of the COIL Laboratory in Prague to the chemical oxygen-iodine laser research and development

The key results gathered in the COIL Laboratory of the Institute of Physics AS in the Czech Republic since 1985 to date on the experimental and theoretical investigation of Chemical Oxygen-Iodine Laser (COIL), and related problems are reviewed in a certain context of historical perspectives of the COIL research and development.

Chemical generation of atomic iodine for COIL

A method of the chemical production of atomic iodine aimed for application in COIL was studied experimentally. The method is based on chemical generation of chlorine atoms and their subsequent reaction with hydrogen iodide. Effects of initial ratio of reactants and the way of their mixing were investigated and interpreted by means of the developed model of the reaction system. In optimum conditions, the yield of iodine atoms, related to HI, attained 70 - 100 percent.