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- The First 25 Years of COIL: Part I
- Poster Session
- The First 25 Years of COIL: Part II
- Other Chemical Lasers
- 2002-Twenty Five Years of COIL: Part III
- Other Chemical Lasers
- Laser Systems, Modeling, and Interactions
- Poster Session
The First 25 Years of COIL: Part I
Historical perspective of COIL
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The oxygen-iodine laser was the first electronic transition chemical laser. It first lased 25 years ago at the Air Force Weapons Laboratory. The development started several years earlier and involved the support of many people in the laser community. I would like to describe the early thoughts, insights and even misconceptions that we had in the early days. I will also highlight the contributions of many of the people and organizations that contributed to the early development of the COIL laser.
Mechanism and kinetics of iodine dissociation in COIL
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Dissociation of I2 by O2(a1D), with subsequent excitation of I*, was first observed by Arnold et al.1 in 1966. This key discovery led to the eventual development of the chemical oxygen iodine laser (COIL). The mechanism by which I2 is dissociated was not determined by Arnold et al.1 and has remained elusive, despite many experimental attempts to unravel this question. Although the details are not known, it is apparent that a complex interplay between vibrationally and electronically excited states of I2 is involved. Vibrationally excited states of O2 have also been implicated. Characterization of the dissociation process is an important issue for COIL as the efficiency is impacted by the energy cost of dissociating the iodine. In this paper we provide a historical summary of work on the dissociation mechanism, and summarize the current understanding of the problem.
Gain and temperature in a slit nozzle supersonic chemical oxygen-iodine laser with transonic and supersonic injection of iodine
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Spatial distributions of the gain and temperament across the flow were studied for transonic and supersonic schemes of the iodine injection in a slit nozzle supersonic chemical oxygen-iodine laser as a function of the iodine and secondary nitrogen flow rate, jet penetration parameter and gas pumping rate. The mixing efficiency for supersonic injection of iodine is found to be much larger than for transonic injection, the maximum values of the gain being approximately 0.65 percent/cm for both injection schemes. Measurements of the gain distribution as a function of the iodine molar flow rate nI2 were carried out. For transonic injection the optimal value of nI2 at the flow centerline is smaller than that at the off axis location. The temperature is distributed homogeneously across the flow, increasing only in the narrow boundary layers near the walls. Opening a leak downstream of the cavity in order to decease the Mach number results in a decrease of the gain and increase of the temperature. The mixing efficiency in this case is much larger than for closed leak.
Chemical generation of atomic iodine for COIL
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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.
Modeling of the chemical generation of atomic iodine in a chemical oxygen-iodine laser
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The mathematical modeling of reaction systems for chemical generation of atomic iodine is presented. This process can 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. The parametric study of the production of atomic fluorine and subsequently atomic iodine in dependence on the pressure and dilution with inert gas was made. The calculation of the interaction between produced atomic iodine and singlet oxygen was made with four different mixing/reacting schemes.
Poster Session
Pulsed COIL with volume generation of iodine atoms in electric discharge
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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.
The First 25 Years of COIL: Part II
German COIL efforts: status and perspectives
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Historically, COIL research in Germany has started with microwave excitation of an oxygen flow. But soon all efforts have been devoted to the chemical generation of excited singlet oxygen and have eventually given rise to a supersonic 10 kW class rotating disk driven device. A diode based diagnostic provides data of small signal gain and cavity temperature which emphasize the role of iodine injection for different penetration conditions. Heat release can lead to substantially higher temperatures as expected from adiabatic expansion. Power extraction is found to be in good agreement with theoretical predictions. Alternatively, small scale liquid jet generator experiments show encouraging 60 percent efficiency. Besides air defense related applications and a study on space debris removal, results are given which are pertinent to the decommissioning of nuclear installations. In particular, laser cutting of concrete at 1.3 micrometers is demonstrated and theoretically scaled up to relevant power levels.
Historical perspective of COIL diagnostics
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In this paper, I present a history of the development of diagnostic techniques for the chemical oxygen iodine laser (COIL). Several established optically based techniques have been applied to COIL including: visible and near infrared chemiluminescence, resonance absorption, and laser induced fluorescence. I trace the history of these developments using the diagnostic methods as the overall theme. In many cases a variant of an established diagnostic was used to probe for some key kinetic rate or mechanism. Indeed, the goal of developing the now well established COIL kinetic rate package was responsible for the introduction of new diagnostic methods. I discuss diagnostics both before and after the demonstration of the first COIL device.
Modeling of the gain, temperature, and iodine dissociation fraction in a supersonic chemical oxygen-iodine laser
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We report on a simple one-dimensional model developed for the fluid dynamics and chemical kinetics in the chemical oxygen iodine laser (COIL). Two different I2 dissociation mechanisms are tested against the performance of a COIL device in our laboratory. The two dissociation mechanisms chosen are the celebrated mechanism of Heidner and the newly suggested mechanism of Heaven. The gain calculated using Heaven's dissociation mechanism is much lower than the measured one. Employing Heidner's mechanism, a surprisingly good agreement is obtained between the measured and calculated gain and temperature over a wide range of the flow parameters. Other predictions of the model (larger mixing efficiency and higher temperature with a leak opened downstream of the resonator and gain decrease along the flow) are also in agreement with the experimental observations.
Contribution of the COIL Laboratory in Prague to the chemical oxygen-iodine laser research and development
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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.
COIL technology development at Boeing
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The historical COIL contributions at the McDonnell Douglas Research Laboratory, the Rocketdyne Division of Rockwell International and Boeing's Laser and Electro-Optic Systems organization are briefly described. The latter organization now contains the capabilities of the two heritage organizations. Boeing's new high pressure sealed COIL is also described.
Other Chemical Lasers
Review of recent experiments and calculations relevant to the kinetics of the HF laser
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An abbreviated review of rate coefficients relevant to HF laser kinetics modeling is presented. The literature has been surveyed from the last published review in 1983 to the present. Updated HF Einstein emission coefficients are tabulated. This brief summary of a more detailed review addresses rate coefficients relevant to HF generation, reactive quenching, self-relaxation, and vibrational relaxation by a selection of atoms and molecules. In addition, a review of recent experiments and theoretical calculations relevant to the role of rotational non- equilibrium in HF lasers is presented. A list of recommended temperature dependent expressions for critical reaction rate coefficients is given.
Tunable solid state laser for HF mirror metrology
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HF mirror metrology is currently costly and time consuming, requiring laser component delivery to an HF laser site, and operation of another HF laser to reach relevant wavelengths. Coherent Technologies, Inc. has developed a solid state Cr:ZnSe laser pumped by a Tm:YALO laser that provides up to 1.1W of output power with 1.1nm linewidth at 2.64micrometers , an HF laser line. The laser can also tune to other HF laser liens in the wavelength range of 2.64micrometers to 2.8micrometers . The Cr:ZnSe laser was used to measure the reflectivity of HF mirror samples provided by TRW. Examples of other possible applications of this source include beam train alignment and preliminary testing of diagnostic subsystems that measure HF laser output power, wavefronts, and beam profiles. Such a direct laser source is simple and can potentially achieve high intensity stability, allowing for a robust and compact HF laser surrogate. Moreover, power scaling is straightforward.
Imaging spectroradiometer for HF laser studies
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We discuss a non-intrusive diagnostic for mixing, species concentration, and optical gain for HF chemical lasers. The instrument is based on hyperspectral imaging using a low order Fabry-Perot interferometer. The basic theory behind this technology is described and several applications to a chemically reacting flowfield are presented.
Room temperature rate constant for H+F2
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The rate constants for H atom reactions with Cl2 and F2 have been measured by monitoring the loss rate of hydrogen atoms in the presence of excess [Cl2] and [F2] via time-resolved, laser-induced Lyman-a fluorescence. The rate constants for H + F2 and H + Cl2 were found to be 2.4 +/- 0.4 X 10-12 and 2.52 +/- 0.18 X 10-11 cm3 molecules-1 s-1, respectively. The result for H + F2 is consistent with the recommendation of Baulch et. al. (J. Phys. Chem. Ref. Data 10 (suppl. 1) (1981)) and our k(H + Cl2) value is consistent with the majority of previous measurements.
2002-Twenty Five Years of COIL: Part III
History of COIL development in Japan: 1982-2002
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A twenty-years of COIL researches and developments in Japan are reviewed. The researches of four major sites, namely, Keio University, Industrial Research Institute, Kawasaki Heavy Industries and Tokai University are presented in order of time. Epoch-making works are highlighted, and the significance of those works in the industrial COIL development is discussed, Finally, current status of COIL researches in Japan is introduced.
High-power COIL and YAG laser welding
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We have constructed a laser welding system, which enabled high-power laser welding by combining three laser beams of 1 mm wavelength. Its wavelength enables optical silica fibers transmission and the flexible system. The heart of this system consists of a 4 kW and a 6 kW Nd:YAG lasers and a 10 kW Chemical Oxygen-Iodine Laser (COIL). The average power of the combined beam is up to over 20 kW. The effects of various welding parameters were investigated, such as the laser power, pulse modulation, and so on. The 10 kW COIL has a very good beam quality which is 64 mm.mrad. The beam spot diameter is 0.48 mm at the focal point. On the contrary the beam quality of Nd:YAG laser is worse, but it has the function of pulse modulation which the COIL dose not have. As a result of the welding test with the 6 kW Nd:YAG laser, it was clarified that the pulse wave (PW) has good efficiency of deeper penetration at low welding speed. When the combined beam with CW COIL and PW Nd:YAG laser was used, 20 mm penetration on the stainless steel could be achieved at a welding speed of 1 m/min.
COIL development in Kawasaki Heavy Industries, Ltd.
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The Chemical Oxygen-Iodine Laser (COIL) has been studied for military use because it has many excellent features. These features count with not only the military but also the industry. The wavelength of COIL 1.315 mm, is a significant features of the industrial laser because it is located in a minimum loss transmission region for optical silica fibers. Therefore, we started the COIL development for industrial use in 1986. In the first stage, we developed a subsonic type. In 1992, the first 1 kW class commercial COIL was delivered. This system was successfully operated for several hours, and its output beam was delivered through the optical silica fiber of 0.3 mm core diameter. But the subsonic COIL has the disadvantage that the device size is relatively large. To solve this problem, the supersonic COIL has been introduced and developed. In 1994, 1 kW supersonic output power was attained. On the basis of this technology, we constructed a 10 kW class in 1996. This system achieved over 12 kW output power and chemical efficiency of 26 percent.
Spatially resolved temperature diagnostic for the chemical oxygen-iodine laser based on a variant of saturation spectroscopy
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The Chemical Oxygen-Iodine Laser (COIL) depends upon a supersonic mixing nozzle to produce optical gain on the 2P1/2 - 2P3/2 atomic iodine transition at l equals 1.315 mm. The translational temperature in the gain generator is particularly important, as the yield of singlet oxygen required to reach lasing threshold decreases from 17 percent at room temperature to 6 percent at T equals 150K. We have demonstrated an optical technique for measuring the gas temperature in the COIL supersonic expansion region with a spatial resolution of less than 12 mm3 using a novel variant of saturated laser spectroscopy. The sub-Doppler hyperfine spectrum of the visible I2 (Chi) 1(Sigma) g+ yields B3(Pi) (Ou+) transition exhibits 15 or 21 transitions and has been recorded using laser saturation spectroscopy with a resolution of about 10 MHz. Pressure broadening of the hyperfine components and cross-relaxation effects have been studied and depend significantly on rotational level. By altering the saturation spectroscopy apparatus so that the pump and probe beams are nearly co-propagating, a Doppler profile, limited to the iodine sample in the volume of the overlapped beams, is obtained. Temperature, as derived from the Doppler profile, is spatially resolved and used to examine the flow from a small supersonic nozzle assembly.
Diagnostic development for the ElectriCOIL flow system
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Detailed studies of mechanisms for producing electrically initiated COIL lasers were previously presented. Results of those studies along with more recent experimental results show that electric excitation is a very complex process that must be investigated with advanced diagnostics. Theoretical studies indicate that fractions of O2(1(Delta) ) may be produced in the discharge that will permit lasing of an ElectriCOIL system. Recent kinetic studies indicate a range of useful operating parameters for ElectriCOIL that are analogous to those achieved in the all-chemical device. This can be accomplished at E/N's in the range of 10-16 Volt-cm2. An experimental test bed has been built up to allow detailed diagnostic measurements of the discharge efficiencies and other experimental parameters. Results of early experiments are presented.
Measurement of chemical oxygen-iodine laser singlet oxygen generator parameter using Raman spectroscopy
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Using a doubled Nd: YAG laser as a spontaneous vibrational Raman scattering source, and a single intensified CCD array at the exit of an imaging monochromator, the Raman scattering system is used to directly measure the concentrations of the O2(a1(Delta) ) and the O2((Chi) 3(Sigma) ) in the chemical oxygen-iodine laser singlet oxygen generator in real time. We present the results from the tests that conducted on a 0.1-mol singlet oxygen-iodine generator. With the current reported uncertainty of the Raman cross-section, the error in the yield measurement is calculated to be less than 8 percent.
Other Chemical Lasers
Tunable diode laser gain measurements of the HF(2-0) overtone transitions in a small-scale HF laser
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A tunable diode laser was used to probe the overtone gain medium of a small-scale HF laser. 2D, spatially resolved small signal gain and temperature maps were generated for the P(3) ro-vibrational transition in the first HF overtone band.
Atomic fluorine source for chemical lasers
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We present results from the early development of an F atom source appropriate for HF and AGIL chemical laser research. The system uses high power microwaves to produce a high enthalpy plasma that thermally dissociates molecular species such as SF6 and F2. Results of the characterization of the flow are presented.
Parametric study of NCl(a1(),NCl(b1()from the reaction of Cl/Cl2/He + HN3/He
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By means of Microwave generator chlorine diluted by helium is dissociated to chlorine atoms that subsequently react with hydrogen azide to produce excited states of NCl(a1(Delta) ) and NCl(b1(Sigma) ). In this paper, the intensity of NCl(a1(Delta) ) and NCl(b1(Sigma) ) emission dependent on the flow rates of different gases is studied. Moreover, the production of NCl(a1(Delta) ) and NCl(b1(Sigma) ) along the reaction tube is also investigated. By using a simple titration method, we obtain the dissociation efficiency of molecular chlorine up to 100 percent at the flow rates of chlorine no more than 1 mmol/s. We also achieve the quenching rate of NCl(a1(Delta) ) by Cl2 is about 4 X 10-13 cm3/sec molec with excess flow rates of chlorine. Finally, the optimum parameters for NCl(a1(Delta) ) and NCl(b1(Sigma) ) production are summarized.
Laser Systems, Modeling, and Interactions
IR- and UV-laser interaction with metal surfaces
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The complex of experimental installations for studying of laser radiation interaction with surface of metals has been established. At titanium surface irradiating depending on the accumulated laser radiation energy, the surface color might be changed from bright yellow to red and deep-blue colors. The presented results testify to the possibility to use the change of titanium surface color at heating by laser irradiation in the open air to obtain dot raster images. Presently, form the world data available on interaction of laser radiation with metal and dielectric surfaces and development of experimental diagnostics techniques by itself it is allowed to raise a reverse question, i.e., restoration of laser radiation energy spatial distribution through surface imprint. Using imprints, it is also possible to make an express diagnostics of multi-layer surface coatings. With this in mind, we have made the detailed morphology of imprint of the pulsed HF-laser interaction with carbon steel surface through atomic force microscope.
Energy transfer dynamics in the A(0u+) state of Bi2
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Laser induced fluorescence, pulsed and CW, techniques have been used to study energy transfer within the A(0u+) state of Bi2. In particular, electronic quenching in the vibrational levels near predissociation, v' equals 18-25, have been examined for rare gas and nitrogen collision partners. The quenching from non-predissociated levels is independent of vibrational state and are rather rapid, 2.3 - 8.5 X 10-11 cm3molecule-s for v' equals 22. The quenching from the first significantly predissociated level, v' equals 23, is even faster with rate coefficients ranging from 7.4 - 15.7 X 10-11 cm3molecule-s. Heterogeneous predissociation is very rapid for 21 -1. Vibrational-to-translational energy transfer probabilities for the lowest vibrational levels, v' equals 0-4, range from 0.75 - 1.75 percent per collision, considerably lower than would be anticipated for these highly non-adiabatic collisions. Spectrally resolved emissions from collisionally populated rotational levels of Bi2(A,v' equals 1) were observed for helium, neon and argon collision partners after laser excitation of the high rotational levels J' equals 171, 201, and 231. Total rotational removal rates from the initially prepared state range from 2.8 - 8.9 X 10-10 cm3molecule-s. Collisional population of rotational states with (Delta) J
Numerical testbed for laser materials processing
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Current numerical simulations of laser materials processing usually simplify any process model to a great extent in order to allow for short computation times. This significantly decreases their flexibility and ability to simulate the great variation of today's processes with their subtle but important differences. The simulation presented in this paper can be said to be truly three dimensional as opposed to other reported work that uses symmetric boundary conditions. This enables the investigators to simulate real laser beams. In contrast to the (well-documented) Marangoni flow profile, the authors will show results that do not use the usual simplifying assumptions of flat surfaces. Preliminary output from the simulation deals with the transient coupled velocity and pressure profile and temperature distribution and hence the heat affected zone (HAZ). From this, conclusions can be drawn with regard to improving process efficiency, especially in laser cutting. It will be shown that the traditional perception of equating higher processing speeds with better processing efficiency does not hold in all cases. In fact, the opposite may well hold true. However, to demonstrate this the actual process of producing a part needs to be fully understood. A process may influence the workpiece material properties beneficially when it is performed at reduced speeds (material hardening or softening). The investigators contend that numerical modeling of the above can only be achieved credibly using high performance computing methods.
High-power-gas-discharge- and laser-plasma-based EUV sources
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In this paper we discuss new results from investigations on high power EUV sources for micro-lithography based on gas discharge produced plasmas and laser produced plasmas. The EUV development is performed at XTREME technologies GmbH, a joint venture of Lambda Physik AG, Goettingen, and Jenoptik LOS GmbH, Jena. For gas discharge EUV sources we report data based on Xenon filled Z-pinches. Prototypes of the EUV source achieve an EUV output power of 10 W in-band in continuous operation. Repetition rates of 1 kHz are possible with liquid cooling of the discharge head. The spectral distribution of the EUV radiation shows a maximum around 13.5 nm and matches the reflection characteristics of silicon/molybdenum multilayer mirrors. Conversion efficiencies between 0.25 percent and 0.7 percent into a solid angle of 2p sr were achieved with the Z-pinch source depending the discharge geometry. The total EUV average power in the spectral range between 5 nm and 50 nm is about 200 W in 1.8 sr. Pulse energy stability data show standard deviation between 1-4 percent. Spatial and temporal emission characteristics of the discharge source in dependence on the discharge geometry are discussed. The laser plasma investigations are performed with an experimental setup consisting of a diode pumped laser system coupled to a liquid jet target. Since the conversion efficiency into EUV-power depends critically on the emitter density in the interaction region, we use a Xenon-jet, which is cryogenically liquefied and injected under high pressure into the vacuum vessel. Thus the laser is impinging on a target of solid-state density, which allows the generation of EUV-radiation with high conversion efficiencies of 0.5 percent into a solid angle of 2p sr.
Poster Session
Observation on laser-induced lens effect in sound generation under water using high-power ultrashort-pulse laser
Huijuan He,
Shaosong Feng
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The ultrashort pulse ofNd:YAG laser system is used to generate the sound in water. The picosecond laser beams are focused at two points in experiments. This effect implies that the time response is inherent due to the changes of index of refraction of water induced by laser beam intensity.
Plasma chemical oxygen-iodine laser: problems of development
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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.