Production of iodine atoms due to dissociation of iodides CF3I, CH3I, C2F5I, and C2H5I in a self sustained pulsed
discharge has been investigated. The efficiency of iodide dissociation as well as a yield of excited iodine atoms has been
measured for different experimental conditions.
The behavior of concentration of iodine atoms produced by a pulsed electric discharge in a mixture of iodide (CF3I,
CH3I) with oxygen was investigated by using a method of absorption spectroscopy. The tunable diode laser was used as
a source of a probe radiation. The significant difference between CF3I, CH3I was observed. The numerical modeling
showed such a difference can be explained by an influence of a recombination process of iodine atom and radical RO2.
The active medium of a pulsed DOIL with volume generation of iodine atoms was experimentally simulated
using the chemical generator of singlet oxygen and MW discharge to understand the feasibility of a pulsed oxygen-iodine
laser with electrical generator of singlet oxygen.
Experimental and theoretical study of influence of nitrogen oxides NO and NO2 admixtures in oxygen containing gas
mixture excited by pulsed electron-beam sustained discharge on input energy and time behavior of singlet delta oxygen
(SDO) luminescence was carried out. Temperature dependence of the constant of SDO relaxation by unexcited
molecular oxygen was estimated.
KEYWORDS: Oxygen, Chemical species, Iodine, Pulsed laser operation, Molecules, Chemical oxygen iodine lasers, Information operations, Plasma, Ionization, Laser energy
Pulsed discharge is effective means to achieve high-peak lasing in COIL. Numerical model is developed for simulation
of pulsed discharge in gas stream from the singlet oxygen generator mixed with CF3I. The model comprises a system of
kinetic equations for neutral and charged species, electric circuit equation, and gas thermal balance equation. Sources of
iodine atoms under discharge and post-discharge conditions are analyzed. The dominant source in the discharge is
electron-impact dissociation of CF3I molecules. In post-discharge phase chemical reactions are identified giving notable
input into I production. Deformation of laser pulse waveform observed experimentally is explained by influence of these
reactions.
Influence of nitrogen oxides NO and NO2 on specific input energy (SIE) and time behavior of singlet delta oxygen
(SDO) luminescence excited by pulsed e-beam sustained discharge in oxygen was experimentally and theoretically
studied. NO and NO2 addition into oxygen results in small increase and decrease of SIE, respectively, the latter being
connected with large energy of electron affinity to NO2. The addition of 0.1-0.3% nitrogen oxides was experimentally
and theoretically demonstrated to result in notable enhancement of SDO lifetime, which is related to a decrease of
atomic oxygen concentration in afterglow. There was experimentally demonstrated that for getting high SDO
concentration at gas pressure 30-60 Torr for the time interval less than ~0.5 s one needs to add not less than 0.2%
nitrogen oxides into oxygen. Temperature dependence of relaxation constant for SDO quenching by unexcited oxygen
was estimated by using experimental data on time behavior of SDO luminescence.
The pulse mode of operation of the chemical oxygen iodine laser (COIL) is attractive for a large body of new
applications. Pulsed electric discharge is most effective to turn COIL operation into the pulse mode by instant
production of iodine atoms. Numerical model is developed for simulations of the pulsed COIL initiated by 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 recalculated 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, 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. The conclusion is drawn about satisfactory agreement of the theory with the
experiment. The mechanisms of iodine atoms production in the pulsed discharge are identified.
Singlet delta oxygen O2a1&Dgr;g (SDO) production in a slab discharges ignited in oxygen gas mixtures was experimentally studied. An influence of gas mixture content and input electric power on SDO yield was analyzed. In self-sustained RF slab discharge SDO yield of 10±5 % was measured by comparison luminescence intensity of SDO going from a chemical generator and SDO generated in electric discharge. SDO yield of 7.2 % was measured by intracavity laser spectroscopy method. It was demonstrated that the choice of electrodes material is very important. Experiments on SDO production in slab non-self-sustained discharge with external ionization by repeating high-voltage pulses were carried out. SDO concentration was measured by the method of intracavity laser spectroscopy. The measured concentration of SDO was about 1.5×1016 cm-3, with SDO yield of ~10.6 %. A development of electric discharge oxygen-iodine laser with SDO production in long electrodes slab discharge is discussed.
Admixing of iodide to the effluent of MW discharge in oxygen was used to measure yield of singlet oxygen generated.
Singlet oxygen yield was evaluated using the equilibrium condition. The method was absolutely calibrated using a
traditional chemical singlet oxygen generator.
Singlet delta oxygen O2(a1Δg) (SDO) production in a slab discharges ignited in oxygen gas mixtures was experimentally
studied. An influence of gas mixture content and input electric power on SDO yield was analyzed. In self-sustained RF
slab discharge SDO yield of 10±5% was measured by comparison luminescence intensity of SDO going from a
chemical generator and SDO generated in electric discharge. SDO yield of 7.2% was measured by intracavity laser
spectroscopy method. It was demonstrated that the choice of electrodes material is very important. Experiments on SDO
production in slab non-self-sustained discharge with external ionization by repeating high-voltage pulses were carried
out. SDO concentration was measured by the method of intracavity laser spectroscopy. The measured concentration of
SDO was about 1.5 1016 cm-3, with SDO yield of ~10.6%. A development of electric discharge oxygen-iodine laser with
SDO production in long electrodes slab discharge is discussed.
Singlet delta oxygen O2(a1Δg) (SDO) production in a slab discharges ignited in oxygen gas mixtures was experimentally studied. An influence of gas mixture content and input electric power on SDO yield was analyzed. In self-sustained RF slab discharge SDO yield of 10±5% was measured by comparison luminescence intensity of SDO going from a chemical generator and SDO generated in electric discharge. SDO yield of 7.2% was measured by intracavity laser spectroscopy method. It was demonstrated that the choice of electrodes material is very important. Experiments on SDO production in slab non-self-sustained discharge with external ionization by repeating high-voltage pulses were carried out. SDO concentration was measured by the method of intracavity laser spectroscopy. The measured concentration of SDO was about 1.5 1016 cm-3, with SDO yield of ~10.6%. A development of electric discharge oxygen-iodine laser with
SDO production in long electrodes slab discharge is discussed.
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.
Absorption spectra of chemically produced singlet oxygen O2(α1Δg) in the vicinity of 1.91 μm wavelength were recorded by intracavity laser spectroscopy technique. The line strengths for Q-branch transitions of the (0,0) band of the b1Σg-α1Δg system were measured. Measurements of the O2(α1Δg) yield for an electric discharge are presented.
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.
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).
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.
Pulsed mode makes COIL possible to produce pulses which power can significantly exceed that of CW COIL mode at the same flowrate of chemicals. Such a mode can find application in material treatment, in drilling for oil wells, as an optical locator, in laser frequency conversion via non-linear processes, in laser propulsion, etc. The method of volume generation of iodine atoms was shown to be the most effective one in generation of high power pulses. The base of method is substitution of molecular iodine in operation mixture for iodide which is stable in the mixture with singlet oxygen, and subsequent forced dissociation of iodide. In this approach the advantage of direct I-atom injection in laser active medium is demonstrated. The comparison of experimental results obtained with different sources used for iodide dissociation shows the electric discharge provides significantly higher electrical laser efficiency in comparison with photolysis initiation. At the same time, the specific energy of the electric discharge initiated COIL is at disadvantage in relation with that obtained with photolysis initiation. This fact is a result of active medium temperature increase due to insufficient initiation selectivity of electric discharge. Both longitudinal and transverse electric discharges were investigated as possible sources for laser initiation. The transverse discharge is more promising for increased operation pressure of active medium. The operation pressure is limited by dark reaction of iodide with singlet delta oxygen. The repetitively pulsed operation with repetition rate of up to 75 Hz of pulsed COIL is demonstrated.
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.
Chemical Oxygen-Iodine Laser operating in a pulsed mode makes it possible to generate pulses with power significantly exceeding the average laser power. Such a mode can find an application in processes in which the power is a crucial factor. They are ablation, cutting, frequency conversion due to nonlinear processes, etc. The different approaches can be used to obtain pulsed COIL operation. The Q-switch method, pulsed singlet oxygen generation and volume instantaneous generation of atomic iodine will be considered. The merits and demerits of every method are discussed below. The recent results on pulsed COIL are presented too.
KEYWORDS: Oxygen, Iodine, Plasma, Chemical oxygen iodine lasers, Chemical lasers, Ionization, Laser development, Molecules, Gas lasers, Chemical species
Great success has been obtained in the R&D of a chemical oxygen-iodine laser (COIL) operating on the electronic transition of the iodine atom, which gets an excitation from the energy donor -singlet delta oxygen (SDO). The latter is normally produced in a chemical SDO generator using very toxic and dangerous chemicals, which puts a limit for civilian applications of COIL that is still a very unique apparatus. Totally new non-chemical SDO generator is needed to allow oxygen-iodine laser to achieve its full potential as a non-hazardous efficient source of high-power laser radiation. There was interest in producing SDO in electric discharge plasma since the 50's long before COIL appearing. The idea of using SDO as a donor for iodine laser was formulated in the 70's. However, the injection of iodine molecules into a low- pressure self-sustained discharge did not result in iodine lasing. One of the main factors that could prevent from lasing in many experiments is a rather high threshold yield ~15% at 300K, which is needed for obtaining an inversion population. An analysis of different attempts of producing SDO in different kinds of electric discharge plasma has been done which demonstrates that high yield at gas pressure of practical interest (p > 10 Torr) for modern COIL technology can be obtained only in non-self sustained electric discharge plasma. The reason is that the value of relatively low reduced electrical field strength E/N ~10-16 V.cm2, which is an order of magnitude less than that for the self-sustained discharge, is extremely important for the efficient SDO production. Although different kinds of non-self sustained discharges can be used for SDO production, we got started experiments with e-beam sustained discharge in gas mixtures containing oxygen. High specific input energy up to ~3 - 5 kJ/l. atm [O2] has been experimentally obtained. Theoretical calculations have been done for different experimental conditions indicating a feasibility of reasonable SDO yield. Experimental and theoretical research of self-sustained electric discharge in SDO produced in a chemical generator, which is very important for getting plasma-chemical kinetic data needed for an estimation of SDO yield, is also discussed.
The method of volume generation of iodine atoms to obtain the pulsed mode of COIL is the most effective by the ratio of pulsed power to cw one at the same flowrate of chemicals. The electric discharge is a very convenient tool to produce iodine atoms in an active medium. The electrical efficiency close to 100% was obtained when longitudinal glow discharge was used. The investigation of both influence of the discharge gap length on the performance of pulsed COIL initiated with longitudinal discharge and transverse discharge initiated pulsed COIL based on the Jet Singlet Oxygen Generator were performed. The lasing of Jet SOG based pulsed COIL has been obtained for the first time. The operation pressure of 17 Torr at oxygen partial pressure of 7 Torr in the laser cavity has been obtained The temperature parameters of active medium being under electric discharge initiation were analyzed. The active medium temperature growth was shown to be responsible for decrease of specific output energy in discharge initiated COIL unlike that for photolytic initiation.
Great success has been obtained in the R&D of a chemical oxygen-iodine laser (COIL) operating on the electronic transition of the iodine atom, which gets an excitation from the energy donor -singlet delta oxygen (SDO). The latter is normally produced in a chemical SDO generator using very toxic and dangerous chemicals, which puts a limit for civilian applications of COIL that is still a very unique apparatus. Totally new non-chemical SDO generator is needed to allow oxygen-iodine laser to achieve its full potential as a non-hazardous efficient source of high-power laser radiation. There was interest in producing SDO in electric discharge plasma since the 50's long before COIL appearing. The idea of using SDO as a donor for iodine laser was formulated in the 70's. However, the injection of iodine molecules into a low- pressure self-sustained discharge did not result in iodine lasing. One of the main factors that could prevent from lasing in many experiments is a rather high threshold yield approximately 15 percent at 300K, which is needed for obtaining an inversion population. An analysis of different attempts of producing SDO in different kinds of electric discharge plasma has been done which demonstrates that high yield at gas pressure of practical interest for modern COIL technology can be obtained only in non-self sustained electric discharge plasma. The reason is that the value of relatively low reduced electrical field strength E/N approximately 1E-16 V.cm2, which is an order of magnitude less than that for the self-sustained discharge, is extremely important for the efficient SDO production. Although different kinds of non-self sustained discharges can be used for SDO production, we got started experiments with e-beam sustained discharge in gas mixtures containing oxygen. High specific input energy up to approximately 3 - 5 kJ/ has been experimentally obtained. Theoretical calculations have been done for different experimental conditions indicating a feasibility of reasonable SDO yield. Experimental and theoretical research of self-sustained electric discharge in SDO produced in a chemical generator, which is very important for getting plasma-chemical kinetic data needed for an estimation of SDO yield, is also discussed.
So far the impressive successes are obtained in development of continuous-wave chemical oxygen-iodine lasers (COIL). But some applications require the laser operating in a pulse mode and generating the power as high as possible. It is known the COIL with volume instantaneous generation of atomic iodine generates the pulses which power is several orders of magnitude higher that of CW mode at the same flow rate of chemicals. More increase of output power can be obtained by using Q-modulation. For efficient extraction of stored energy the frequency of modulation should be as high as reciprocal time of inversion population recover. i. e. megahertz scale. Such a high modulation frequency can be produced with electrooptic or acousto-optic modulator (AOM). The experimental results of application of AOM to pulsed COIL with a discharge pulsed generation of atomic iodine are presented. The AOM power supply allows one to vary the temporal parameters of modulation. The laser generates a train of pulses with the given duration and repetition rate. Experiments show that optimization oftemporal parameters of modulation is required
KEYWORDS: Pulsed laser operation, Continuous wave operation, Iodine, Chemical oxygen iodine lasers, Chemical species, Oxygen, High power lasers, Optical simulations, Bragg cells, Chemical lasers
The processes governing the operation of both the pulsed COIL with a forced homogeneous generation of atomic iodine and the premixed I2-dissociated continuous-wave laser are identical. It makes it possible to use a pulsed laser with a low chlorine flowrate to simulate the high power CW operation and to predict its performance. The examples of such predictions made for famous CW laser systems 'RADICL' and 'RotoCOIL1' are presented and discussed. Experimental results on application of AOM for generation of a train of microsecond pulses are also presented.
Pulsed chemical oxygen-iodine laser with a discharge generation of atomic iodin is described. Having the output energy like that with photolysis iodine atoms generation such a laser exhibits higher plug-in efficiency. The efficiency value of 91% is reported. Pulse power of 100 kW was obtained which exceeds two orders of magnitude that for cw laser with the same chlorine flowrate. Repetitively pulsed operation is reported.
KEYWORDS: Oxygen, Chemical oxygen iodine lasers, Iodine, Pulsed laser operation, Chemical lasers, Fusion energy, Chemical species, Chlorine, Signal processing
The pulsed operation of COIL is now a subject of interest. The different approaches are used to obtain such a mode. The method of instant volumetric iodine generation is considered. The experimental results are presented. The advantage and disadvantages, problems, perspectives and possible applications are discussed.
KEYWORDS: Oxygen, Chemical oxygen iodine lasers, Iodine, iodine lasers, Pulsed laser operation, Chemical species, Transmittance, Chemical analysis, Amplifiers, Chemical lasers
Intensive Investigation and developmentof the chemically pumped Iodine laser has caused the creation by Kawasaiw of chemical oxygen Iodine laser (COiL) for material processing. The field of such a laser application could be widen if the pulse operation would be available. Such a regime allows to hightert the instant power of COIL with the average power being the same as for CW operation. The high instant power can be more preferable for such technological processes as drilling, cutting, ste.
The features of the pulsed chemical oxygen-iodine laser operation are discussed. It is noted that alkyliodides are preferable iodine donors in the case of the chlorineless mixture of RI and singlet oxygen. The fast deactivation of the singlet oxygen by RO2 is a limiting factor when perfluoroalkyliodides are used as iodine donors.
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