Andrei A. Kotkov

The methods of singlet oxygen detection for DOIL program

The problem of development of a singlet delta oxygen O2(1Δg) (SDO) generators alternative to chemical one needs application of the accurate methods of measuring the SDO concentration. A chemical SDO generator providing efficient operation of a chemical oxygen-iodine laser (COIL) is proposed to be used as a reference source for absolute calibration of the system measuring the SDO concentration. The principle of the COIL operation results in the threshold and output COIL parameters make it possible to evaluate the SDO yield with a satisfactory accuracy. A convenient sparger chemical SDO generator was applied as a reference source for absolute calibration of detectors of dimole (λ=634nm) and b→X (λ=762 nm) radiations. The values of b-state concentration formed in a longitudinal electric discharge were evaluated. The intracavity laser spectroscopy (ICLS) was absolutely calibrated for measuring the SDO concentration. ICLS method has a very high sensitivity and makes it possible to monitor the absorption corresponding to the O2(1Δg)→O2(1Σg+) (λ = 1.91 μm) transition. The cross-sections of lines of the Q - branch of the vibrational 0-0 band of the a1Δg → b1Σg+ transition of molecular oxygen were measured. The method developed was applied to measure the concentration of singlet oxygen produced in the microwave discharge. He - Ne laser (λ = 633 nm) was used for absolute calibration of a system monitoring the dimole radiation. The rate constant of the process responsible for dimole emission was measured. The value obtained kd=7.34•10-23 cm3/s is in agreement with literature.

Singlet delta oxygen production in e-beam sustained discharge: theory and experiment

Singlet delta oxygen (SDO) production in a pulsed e-beam sustained discharge (EBSD) ignited in molecular oxygen with carbon monoxide stabilizing this discharge is theoretically and experimentally studied. Temporal behavior of SDO concentration and yield in the EBSD afterglow is analyzed. Experimentally measured SDO yield for oxygen mixture O2:Ar:CO=1:1:0.05 at total gas pressure 30 Torr comes up to 7% at specific input energy (SIE) of ~3.0 kJ/(1 atm(O2+CO)), whereas its theoretical value riches ~ 17.5%. The efficiency of SDO production is theoretically analyzed as function of the SIE.

Theoretical studies on kinetics of singlet oxygen in nonthermal plasma

An idea to replace singlet delta oxygen (SDO) generator working with wet chemistry by electric discharge generator has got much attention last years. Different kinds of discharge were examined for this purpose, but without a great success. The existing theoretical models are not validated by well-characterized experimental data. To describe complicated kinetics in gas discharge with oxygen one needs to know in detail processes involving numerous electronic excited oxygen molecules and atoms. To gain new knowledge about these processes experimental studies were made on electric discharge properties in gas mixture flow with independent control of inlet SDO concentration. The theoretical model extended to include minor additives like oxygen atoms, water molecules, ozone was developed. Comparison with careful experimental measurements of electric characteristics along with gas composition allows us to verify the model and make theoretical predictions more reliable. Results of numerical simulations using this model for an electron-beam sustained discharge are reported and compared with the experimental data.

Supersonic electron beam controlled discharge CO laser

An electron-beam controlled discharge (EBCD) supersonic CO-laser operating at transient conditions of excitation (?dis /?tr~1) has been investigated. Mach number equaled 3.0. The e-beam current density was 1 mA/cm2 . The discharge has been excited between two electrodes spaced 41 mm. The axis of the main resonator has been shifted from the discharge region centre by 120 mm downstream. Small additions of H2 (1-2%) into CO:N2: Ar gas mixture resulted in the increase of a specific input energy, but the efficiency has been reduced. Maximum efficiency reached 20 % . The output peak power has been gradually growing with the growth of the gas density,and reached 90 kW ( the gas density being 0.5 Amagat ). Five additional cavities have been placed downstream. The usage of the cavities has allowed us to measure the lifetime of the inverse population in CO:N2: Ar mixtures.

Quantitative spectroscopic atmospheric pollution diagnostics using first-overtone CO laser radiation

Optimum spectral regions are selected for absorption diagnostics of 38 organic and inorganic atmospheric pollutants in the range of 2.5-4.2 micrometers . Computer code ANLINES is developed and numerical simulation of multicomponent spectra is made. Sounding frequencies for diagnostics of 7 inorganic gases with using first-overtone CO laser and HF/DF lasers are selected. Different parameters of sensitivity and selectivity are discussed: minimum detectable concentrations, partial sensitivities, partial selectivities, cross sensitivities. The comparison of these parameters is made for first-overtone CO and HF/DF lasers.

Electron-beam sustained discharge in oxygen gas mixtures: singlet delta oxygen production for oxygen-iodine laser

Electric properties and spectroscopy of an e-beam sustained discharge (EBSD) in oxygen and oxygen gas mixtures at gas pressure up to 100 Torr were experimentally studied. The pulsed discharge in pure oxygen and its mixtures with noble gases was shown to be very unstable and characterized by low input energy. When adding small amount of carbon monoxide or hydrogen, the electric stability of the discharge increases, specific input energy (SIE) per molecular component being more than order of magnitude higher and coming up to 6.5 kJ/(l atm) for gas mixture O2:Ar:CO = 1:1:0.1. The results of experiments on spectroscopy of the singlet delta oxygen O2(a1Δg)(SDO) and O2(b1Σg+) states in the EBSD are presented. The calibration of the optical scheme for measuring the SDO absolute concentration and yield using the detection of luminescence of the SDO going from a chemical SDO generator was done. The preliminary measurement of the SDO yield demonstrated that it was ~3% for the SIE of ~1 kJ/(l atm), which is close to the results of theoretical calculations for such a SIE. Theoretical calculations demonstrated that for the SIE of 6.5 kJ/(l atm) the SDO yield may reach ~20% exceeding its threshold value needed for oxygen-iodine laser operation at room temperature, although a part of the energy loaded into the EBSD goes into the vibrational energy of the molecular admixture, (which was experimentally demonstrated by launching a CO laser operating on an oxygen-rich mixture O2:Ar:CO = 1:1:0.1 and measuring its small-signal gain).

Detection capabilities of different molecular lasers in infrared spectroscopic diagnostics of multicomponent gas mixtures

The capabilities of different molecular gas lasers in infrared absorption diagnostics of multicomponent mixture are evaluated and compared. Extended sets of vibration-rotational emission lines are used for the following lasers: CO2, HF, DF, NH3, N2O and CO (including fundamental and first overtone transitions). Analytical frequencies are selected for all indicated lasers using spectroscopic databases in order to detect organic and inorganic pollutants using either low- or high-resolution spectra. Comparison of absorption in the atmosphere is made for frequencies of different lasers. Absorption spectra are simulated for 38 component gas mixture. Quantitative parameters characterizing the sensitivity and the selectivity of specific gas detection are calculated and compared: minimum detectable concentration, partial sensitivity, partial selectivity. It is found that NH3 and CO lasers presently have the best spectroscopic detection characteristics.

Electric properties, spectroscopy, and singlet delta oxygen yield of electron-beam sustained discharge in oxygen gas mixtures

Electric properties and spectroscopy of an e-beam sustained discharge (EBSD) in oxygen and oxygen gas mixtures at gas pressures up to 100 Torr was experimentally studied in large excitation volume (~18 liter). The discharge in pure oxygen and its mixtures with noble gases was shown to be very unstable and characterized by low input energy. When adding small amount of carbon monoxide or hydrogen, the electric stability of the discharge increases, specific input energy per molecular component being higher more than order of magnitude and coming up to 6.5 kJ/(l atm). Theoretical calculations demonstrated that for the experimental conditions the singlet delta oxygen yield may reach ~20% exceeding its threshold value needed for oxygen-iodine laser operation at room temperature. The results of experiments on spectroscopy of the singlet delta and singlet sigma oxygen states in the EBSD are presented.

Diagnostics of turbulent flow parmeters of active mixture in fast axial flow CO2 laser

The characteristics of turbulent flow of laser mixture in high-power industrial CO2 lasers with fast axial flow have an influence on energy parameters of laser beam. In particular the transverse size of DC discharge and discharge stability depend on coefficient of turbulent diffusion. Moreover, turbulent pulsations cause small-scale optical inhomogeneities in the active medium. By the method of intra-resonator four-wave mixing in the active mixture of industrial CO2 laser with fast axial flow the coefficient of turbulent diffusion was determined. The nonlinearity of gain coefficient was used, and dissipation of amplitude diffraction grating due to turbulent diffusion was taken into consideration.

Effective multiline pulsed first-overtone CO laser operating in a spectral range of 2.5 to 4.1 μm

Output characteristics of a pulsed e-beam controlled discharge laser operating on the first-overtone (FO) transitions (?V=2) of CO molecule have been studied both experimentally and theoretically. Various sets of dielectric mirrors with high reflectivity in the range of the overtone spectrum have been used for the laser resonator. Multiwavelength lasing has been obtained in the wide spectral range of 2.5 - 4.1 µm on vibrational transitions from 6?4 up to 37?35. Maximum output efficiency as high as 11% has been experimentally obtained for the broad band FO CO laser. Output efficiency of the laser operating on a few vibrational bands within the relatively narrow spectral range 2.5-2.7 µm comes up to 5% at entirely suppressed fundamental band (?V=1) lasing. FO CO lasing was observed within an initial gas temperature interval of 100-220 K. Spectral characteristics of the overtone laser operating on a selected set of vibrational bands have been analyzed theoretically. Theoretical calculations based on the experimental data predict that multiline FO CO laser efficiency can be increased up to 20%.