Nikolay I. Ufimtsev

Efficient subsonic chemical oxygen-iodine laser operating without buffer gas

Efficient subsonic chemical oxygen iodine laser operating with small buffer gas flow rate at Mach number M<EQ1 is reported. The highest value of output power of 415 W with chemical efficiency 23% was obtained at Cl2 flow rate of 20 mmole/s. It was found that the power does not almost depend on N2 or CO2 buffer gas flows up to two times higher than oxygen flow rate.

Predicted and measured output parameters of high pressure jet SOG

Jet singlet oxygen generator (JSOG) is one of the most efficient sources of electronically excited O2(1(Delta) ). The JSOG can operate at very high partial O2(1(Delta) ) pressure. This feature of JSOG allows supersonic COIL operation without water vapor trap. The prediction of output parameters of JSOG is very important for correct design and engineering of COIL. The one-dimensional model of JSOG has been developed to predict output parameters (chlorine utilization, O2(1(Delta) ) yield). The comparisons of calculated and measured output parameters are presented. The main attention is paid to discrepancies of calculated and measured output parameters and limitation of the one-dimensional model. It is shown that for extremely high pressure JSOG the role of effects that cannot be included into a one-dimensional model is very important. The difference between input and output BHP temperature in JSOG is correlated with chlorine utilization and O2(1(Delta) ) yield.

Tunable diode-laser spectroscopy (TDLS) of 811.5nm Ar line for Ar(4s[3/2]2) number density measurements in a 40MHz RF discharge

A hardware and a computative technique for tunable laser spectroscopy was developed for simultaneous measurement of Gaussian and Lorentian components of line broadening by fitting Voigt line profile. The technique was tested in measurements of pressure broadening coefficient for 811.5 nm Ar absorption line in a 40 MHz discharge in the pressure range 15-75 Torr with the help of tunable diode laser with a short external resonator. The obtained values for this coefficients reduced to 300 K are: ξAr-Ar = (2.85±0.1)×10-10 s-1cm3 for broadening in the parent gas and ξAr-He = (3.3±0.1)×10-10 s-1cm3 for broadening in helium. A good agreement with published results is observed. Measured Ar(1s5) number density amounted to 10-11cm-3 for the discharge power density ~10 W cm-3.

Properties of a DC glow discharge iodine atom generator

Concentration of iodine molecules at the outlet of an electric discharge iodine atoms generator was measured using laser-induced fluorescence. Methyl iodine was used as an iodine atom precursor. Fraction of iodine extracted from CH3I in the discharge generator was about 50%. Optimal mode of operation at which 80-90% of total extracted iodine was in the form of iodine atoms was found. Iodine atom content in the gas flow decreased during transportation down to 20-30% at the point of iodine injection into the oxygen flow. Fraction of power load spent on CH3I dissociation amounted to ≈3%.

Effective operation of subsonic COIL with N 2 and CO 2 buffer gases

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%.

Oxygen-iodine active medium with external production of iodine in a DC glow discharge

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.

Calculation of O2 molecules distribution over vibrational levels in chemical oxygen-iodine laser

The kinetics model of chemical oxygen-iodine laser (COIL) active medium taking into account EE, EV, VV, VT energy transfer processes was proposed. The O2 molecule distribution on the vibrational levels in COIL was calculated. It is suggested that the involving of vibrationally excited O2(a) into pooling reaction can increase the rate of stored in singlet oxygen electronic energy in COIL medium. Approximately 50% of relaxed O2(a) energy transfers into thermal energy.

Influence of molecular oxygen on iodine atoms production in an RF discharge

The results of the experiments and modeling of CH3I dissociation in a 40 MHz RF discharge plasma are presented. A discharge chamber of an original design, consisting of quartz tubes between two planar electrodes, permitted us to produce iodine atoms with a number density up to 2 × 1016 cm−3. In this discharge chamber, contrary to the previous experiments with a DC discharge and RF discharge with bare planar electrodes, contamination of the walls of the tubes did not disturb discharge stability, thus increasing iodine production rate. A substantial increase in CH3I dissociation efficiency due to the addition of oxygen into Ar(He) : CH3I mixtures was observed. Complete CH3I dissociation in the Ar : CH3I : O2 mixture occurred at 200 W discharge power, while a fraction of discharge power spent on iodine atoms production at 0.17 mmol s−1 CH3I flow rate amounted to 16%. Extensive numerical modeling showed satisfactory agreement with the experiments and permitted us to estimate a previously unknown rate of constants for the processes: Ar* + CH2I2 → Ar + CH2 + I + I – 1.5 × 10−11 cm3 s−1; Ar* + CH2I2 → Ar + CH2I+ + I + e – 10−11 cm3 s−1. Also, the cross section for the process CH2I2 + e → CH2 + I + I + e was estimated to be five times smaller than for the analogous process with CH3I.

Plasma chemistry of iodine atoms production for CW oxygen-iodine laser

Usage of iodine atoms instead of molecules in oxygen-iodine laser permits to expand its range of operation parameters and improve the weight per power ratio. Results of experiments and modeling of plasma chemistry processes resulting in CH3I dissociation in a planar 40 MHz discharge are presented, showing that addition of oxygen or water into Ar:He:CH3I mixtures can lead to a noticeable increase in CH3I dissociation rate and inhibit iodine recombination during transport.

Pressure broadening coefficients for the 811.5 nm Ar line and 811.3 nm Kr line in rare gases

This paper describes systematic measurements of pressure broadening coefficients for argon and krypton lines in an RF (radio-frequency) discharge plasma sustained in a mixture of inert gases. Using tunable diode laser spectroscopy we obtained experimental data for pressure broadening of argon and krypton lines. Pressure broadening coefficients were determined for Ar+Ne and Kr+Ne and Kr+Ar. For krypton, the isotopic structure of the line was taken into account and an appropriate fitting function was used to determine pressure broadening coefficients for the natural mixture of isotopes. These data may be used for diagnostics of the active medium of optically pumped all-rare-gas lasers.