Pulsed Chemical Oxygen-iodine Laser Research Articles

The Dynamics and Characteristics of the Pulsed Discharge in the Active Medium of a Pulsed Chemical Oxygen-Iodine Laser

In this article, a one-dimensional self-consistent hybrid model of fluid and kinetics is developed to simulate the pulsed discharge occurring in the active medium with a composition CF3I–O2–O2(a1 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\bigtriangleup$ </tex-math></inline-formula> g)–He in a pulsed chemical oxygen-iodine laser (COIL). The iodine atom formation mechanism, the energy exchange between singlet delta oxygen and iodine atom, and the behaviors of various discharge products during the discharge and postdischarge are studied in detail. The dependences of the iodine atom density and energy cost of an iodine atom on the partial pressure ratio of the gas mixture are analyzed and discussed. It is shown that the main channel of iodine atom formation is the electron impact dissociation of CF3I rather than the ionization process. Chemical reaction processes have a small contribution to I atom production, especially the reaction processes involving oxygen. Keeping total pressure and oxygen partial pressure unchanged, there exists an optimum ratio of CF3I:He, at which the highest iodine atom density and the lowest energy cost are achieved. Under simulation conditions, I atom concentration decreases with increasing total operation pressure and oxygen pressure. At constant total pressure and oxygen pressure, when the content of singlet oxygen is lower than 40% of total oxygen pressure, the population inversion cannot be formed.

Efficient pulsed chemical oxygen-iodine laser with instantaneous generation of atomic iodine by volumetric discharge

A pulsed chemical oxygen-iodine laser (COIL) using atomic iodine generated by volumetric discharge of CH3I is developed and tested. COIL with a gain length of 60 cm is energized by a square pipe-array jet singlet oxygen generator with basic hydrogen peroxide pumping circulations and operated at subsonic gas flow. Maximum output energy of 4.3 J, pulse duration of 50 μs, specific energy extraction from the active medium of 2.0 J/L, and the maximum chemical efficiency of 12.5% are achieved at a chlorine flow rate of 55 mmole/s.

Theoretical research of the influence of operation mode of chemical oxygen-iodine laser on its pulsing

One-dimensional pre-mixed model for a pulsed chemical oxygen-iodine laser is presented according to the reaction mechanism in chemical oxygen-iodine laser. The influences of gas temperature of 150-450 K and pressure of 660-2660 Pa on single pulse energy, pulse duration and peak power are studied. The internal reason of the influences of pressure and temperature on laser characteristics is analyzed. The results show that the higher laser peak power can be obtained in the case of gas temperature of 150 K and pressure of 1330 Pa than in the case of 400 K and 2660 Pa. Thus an efficient pulsed chemical oxygen-iodine laser is promising if the abundant atomic iodine is generated instantaneously. The approach to atomic iodine generation does not disturb the state of supersonic flow.

Role of N2 molecules in pulse discharge production of I atoms for a pulsed chemical oxygen–iodine laser

A pulsed electric discharge is the most effective means to turn chemical oxygen–iodine laser (COIL) operation into the pulse mode by fast production of iodine atoms. Experimental studies and numerical simulations are performed on a pulsed COIL initiated by an electric discharge in a mixture CF3I : N2 : O2(3X) : O2(a 1Δg) flowing out of a chemical singlet oxygen generator. A transverse pulsed discharge is realized at various iodide pressures. The model comprises a system of kinetic equations for neutral and charged species, the electric circuit equation, the gas thermal balance equation and the photon balance equation. Reaction rate coefficients for processes involving electrons are repeatedly re-calculated by the electron Boltzmann equation solver when the plasma parameters are changed. The processes accounted for in the Boltzmann equation include direct and stepwise excitation and ionization of atoms and molecules, dissociation of molecules, electron attachment processes, electron–ion recombination, electron–electron collisions and second-kind collisions. The last processes are particularly important because of a high singlet oxygen concentration in gas flow from the singlet oxygen chemical generator. A conclusion is drawn about satisfactory agreement between the theory and the experiment.

Dynamical simulation of pulsed chemical oxygen-iodine laser

One-dimensional pre-mixed model for a pulsed chemical oxygen-iodine laser is presented according to the reaction mechanism in chemical oxygen-iodine laser. The dependence of species concentration and optical parameters on single pulse energy and pulse duration is studied. The dynamical process is analyzed while laser is running. Gain switching during lasing is discussed.These results can provide theoretical support for the optimization of pulsed chemical oxygen-iodine laser.

Analytic study of the chain dark decomposition reaction of iodides — atomic iodine donors — in the active medium of a pulsed chemical oxygen—iodine laser: 2. Limiting parameters of the branching chain dark decomposition reaction of iodides

The final stages in the development of a branching chain decomposition reaction of iodide in the active medium of a pulsed chemical oxygen—iodine laser (COIL) are analysed. Approximate expressions are derived to calculate the limiting parameters of the chain reaction: the final degree of iodide decomposition, the maximum concentration of excited iodine atoms, the time of its achievement, and concentrations of singlet oxygen and iodide at that moment. The limiting parameters, calculated by using these expressions for a typical composition of the active medium of a pulsed COIL, well coincide with the results of numerical calculations.

Analytic study of the chain dark decomposition reaction of iodides — atomic iodine donors — in the active medium of a pulsed chemical oxygen—iodine laser: 1. Criteria for the development of the branching chain dark decomposition reaction of iodides

The scheme of chemical processes proceeding in the active medium of a pulsed chemical oxygen—iodine laser (COIL) is analysed. Based on the analysis performed, the complete system of differential equations corresponding to this scheme is replaced by a simplified system of equations describing in dimensionless variables the chain dark decomposition of iodides — atomic iodine donors, in the COIL active medium. The procedure solving this system is described, the basic parameters determining the development of the chain reaction are found and its specific time intervals are determined. The initial stage of the reaction is analysed and criteria for the development of the branching chain decomposition reaction of iodide in the COIL active medium are determined.

Mechanism of pulse discharge production of iodine atoms from CF3I molecules for a chemical oxygen–iodine laser

The pulsed chemical oxygen–iodine laser (COIL) development is aimed at many new applications. Pulsed electric discharge is most effective in turning COIL operation into the pulse mode by instant production of iodine atoms. A numerical model is developed for simulations of the pulsed COIL initiated by an electric discharge. The model comprises a system of kinetic equations for neutral and charged species, electric circuit equation, gas thermal balance equation and the photon balance equation. Reaction rate coefficients for processes involving electrons are found by solving the electron Boltzmann equation, which is re-calculated in a course of computations when plasma parameters changed. The processes accounted for in the Boltzmann equation include excitation and ionization of atoms and molecules, dissociation of molecules, electron attachment processes, electron–ion recombination, electron–electron collisions, second-kind collisions and stepwise excitation of molecules. The last processes are particularly important because of a high singlet oxygen concentration in gas flow from the singlet oxygen chemical generator. Results of numerical simulations are compared with experimental laser pulse waveforms. It is concluded that there is satisfactory agreement between theory and the experiment. The prevailing mechanism of iodine atom formation from the CF3I donor in a very complex kinetic system of the COIL medium under pulse discharge conditions, based on their detailed numerical modelling and by comparing these results both with experimental results of other authors and their own experiments, is established. The dominant iodine atom production mechanism for conditions under study is the electron-impact dissociation of CF3I molecules. It was proved that in the conditions of the experiment the secondary chemical reactions with O atoms play an insignificant role.

Mechanism of dark decomposition of iodine donor in the active medium of a pulsed chemical oxygen — iodine laser

A scheme is proposed that describes the dark decomposition of iodide — the donor of iodine — and the relaxation of singlet oxygen in the chlorine-containing active medium of a pulsed chemical oxygen — iodine laser (COIL). For typical compositions of the active media of pulsed COILs utilising CH3I molecules as iodine donors, a branching chain reaction of the CH3I decomposition accompanied by the efficient dissipation of singlet oxygen is shown to develop even at the stage of filling the active volume. In the active media with CF3I as the donor, a similar chain reaction is retarded due to the decay of CF3 radicals upon recombination with oxygen. The validity of this mechanism is confirmed by a rather good agreement between the results of calculations and the available experimental data. The chain decomposition of alkyliodides accompanied by an avalanche production of iodine atoms represents a new way of efficient chemical production of iodine for a COIL.

Pulsed chemical oxygen—iodine laser with volume generation of iodine as a model of a high-power supersonic cw laser

In view of the identity of the kinetic processes and of the active-medium parameters of cw and pulsed chemical oxygen—iodine lasers, a repetitively pulsed laser with volume generation of iodine atoms and with a low average output power can be used as a simulator of a high-power cw laser. A comparison is made of experimental results with the parameters of a cw laser predicted by a numerical model.

Pulsed chemical oxygen—iodine laser with bulk formation of iodine atoms by an electric discharge

A preliminary investigation was made of a chemical oxygen—iodine laser with bulk formation of iodine atoms in an electric discharge. The output energy was comparable with that obtained for a photolysis variant of the laser, but the technical efficiency of the investigated discharge variant was much higher (91%). The pulse power (~100 kW) was approximately three orders of magnitude higher than the power of a cw chemical oxygen—iodine laser with the same chlorine flow rate.

Experimental investigation of chemical oxygen-iodine laser

Results of an experimental investigation of a chemical oxygen-iodine laser (COIL) are presented. We determine the factors influencing the efficiency of a chemical singlet-oxygen generator (SOG) of the bubbler type operating on the chlorination of an alkaline solution of oxygen peroxide. We describe SOG constructions. A cw COIL with output power up to 400 W is developed on the basis of the investigated SOG. The feasibility of a modular construction of high-power COIL is demonstrated. A power-output level of 1 kW was achieved with a two-section laser. The feasibility is analyzed of COIL operation in a pulsed regime by pulsed bulk accrual of iodine atoms. We show that in this regime the laser can be operated without a low-temperature trap. An advantage of such a regime is also the possibility of controlling, in a wide range, the lasing pulse duration. A strong influence of molecular chlorine on the energy content of the active medium is observed when alkyliodides are used as iodine donors. The possibilities of using a pulsed COIL for controlled thermonuclear fusion are discussed.

A frequency-doubled pulsed chemical oxygen-iodine laser

The intracavity second-harmonic generation of pulsed chemical oxygen-iodine laser radiation was investigated. A pulsed chemical oxygen-iodine laser with a maximum output energy of 6.14 mJ was used. The second-harmonic output of 0.5 mJ was demonstrated using a lithium iodate crystal. The conversion efficiency of 8% was limited by intracavity losses. Numerical simulation predicts that a conversion efficiency of 75% can be obtained with 1% intracavity losses.

Features of kinetic processes in the active medium of a pulsed chemical oxygen-iodine laser

It can be concluded from our experiments and calculations that the product CF3O2 of the interaction between the CF3 radical and the O2 molecule quenches the oxygen O2(1Δ) more strongly. At low chlorine admixture density in the singlet-oxygen stream this output energy of the oxygen-iodine laser with CF3I as the atomic iodine donor is lower compared with CH3I. The rate constant of quenching singlet oxygen by CF3O2 molecules is (3–5)·10−11 cm3·sec−1. It would be possible to decrease the influence of CF3O2 by adding to the initial O2*−O2−CF3I−Ar active mixture some other substance causing the CF3 radicals to enter in a chemical reaction with a shorter characteristic time than that for CF3O2 formation. Of course, neither the initial substance nor the reaction products should quench O2* noticeably. This role can be possibly assumed by the NO molecule.

Influence of water vapor on the output energy of a pulsed oxygen-iodine laser

Experimental studies showed that the output energy of a pulsed chemical oxygen-iodine laser depended weakly on the partial water vapor pressure in the resonator right up to values which were three times higher than the oxygen pressure, which corresponded to thermally insulated operation of a generator supplying singlet oxygen to the laser.

Molecules of CH3I andn-C3F7I as iodine atom donors in a pulsed chemical oxygen-iodine laser

The laser output energies obtained as a result of photolysis of RI-O2(1Δg)-O2(X3Σg-)-Ar mixtures were determined in a comparison of CH3I and n-C3F7I as donors of atomic iodine in a pulsed chemical oxygen-iodine laser.