Sealed-off CO Research Articles

Plasma chemistry of the sealed-off slab CO laser active medium pumped by radio-frequency discharge with liquid-nitrogen-cooled electrodes

The long-term time behavior of the output power of a sealed-off cryogenic slab CO laser pumped by a repetitively pulsed RF discharge and operating on the overtone (λ = 2.6–3.5 μm) vibrational−rotational transitions of the CO molecule was studied experimentally. It is shown that adding of an anomalously large amount of oxygen (up to 50% with respect to the CO concentration) to the initial gas mixture CO : He = 1 : 10 leads to a manyfold (by several tens of times) increase in the duration of the laser operating cycle (until lasing failure due to the degradation of the active medium). In this case, the laser life-time without replacement of the active medium reaches 105–106 pulses. Using various diagnostics (including luminescence spectroscopy and IR and UV absorption spectroscopy), regularities in the time-behavior of the concentrations of the main component of the active medium (CO molecules) and the products of plasmachemical reactions (O3, CO2) generated in the discharge gap during the laser operating cycle are revealed. Time correlation between the characteristics of the active medium and the laser output power are analyzed. A phenomenological approach to describing the entirety of plasmachemical, purely chemical, gas-dynamic, and diffusion processes determining the behavior of the laser output characteristics throughout the laser operating cycle is offered.

Influence of nitrogen on CO-laser characteristics

The role of the addition of nitrogen to the discharge plasma of CO lasers on plasma-chemical processes is discussed here. It is shown that nitrogen addition improves laser characteristics and changes the composition of the laser active medium. A reduction of CO highly-excited vibrational-states populations with current is smaller in the case of mixtures with nitrogen additions. The addition of nitrogen significantly decreases CO dissociation level and concentrations of C atoms created in plasma-chemical reactions of laser discharge. Full Text: PDF ReferencesG.M. Grigorian and I.V. Kochetov, "Balance of CO molecules in the plasma of a sealed-off CO laser", Plasma Phys. Rep. 30, 788 (2004). CrossRef V.S. Aleinikov and V.I. Masychev, CO Lasers (Moscow, Radio i Svyaz' 1990).A. Cenian, A. Chernukho, V. Borodin and G.Śliwiński, "Modeling of Plasma-Chemical Reactions in Gas Mixture of CO2 Lasers I. Gas Decomposition in Pure CO2 Glow Discharge", Contr. Plasma Phys. 34, 25 (1994). CrossRef A. Cenian, A. Chernukho, V. Borodin, "Modeling of Plasma-Chemical Reactions in Gas Mixture of CO2 lasers. II. Theoretical Model and its Verification", Contrib. Plasma Phys. 35, 273 (1995). CrossRef A. Cenian, A. Chernukho, P. Kukiełło, R. Zaremba, V. Borodin and G. Śliwiński, "Improvement of self-regeneration of gas mixtures in a convection-cooled 1.2 kW laser", J.Phys. D: Appl.Phys. 30, 1103 (1997). CrossRef E.A. Trubacheev, Trudy FIAN 102, 3 (1977).G.M. Grigorian, B.M. Dymshits and Yu.Z. Ionikh, "Influence of oxygen on the parameters of the active medium in an electric-discharge CO laser", Sov J Quant Electron 19, 889 (1989). CrossRef V.N. Ochkin, S.Yu. Savinov, N.N. Sobolev and E.A. Trubacheev, Kvant. Elektr. 1, 573 (1974).

Plasma-chemical processes with the participation of nitrogen in the active medium of a sealed-off CO laser

The influence of the addition of nitrogen to a He–CO mixture on plasma-chemical processes in a discharge under conditions characteristic of the active medium of a sealed-off CO laser was studied. It was found that the addition of nitrogen noticeably decreased the rate of CO dissociation and the concentrations of C atoms and C2 and C3O2 molecules formed in a discharge in the course of plasma-chemical reactions.

Effect of the active medium temperature on the operation of fast-flow CO2 lasers

A new formula is obtained for estimating the output power of fast-flow CO2 lasers. It is shown that a higher specific output power of these CO2 lasers in comparison with sealed-off CO2 lasers is caused mainly by the higher saturation intensity of the former. It is concluded that the temperature of the laser active medium affects almost only the charge stability and that, under stable discharge conditions, the same output power can be obtained at different temperatures of the active medium.

Balance of CO molecules in the plasma of a sealed-off CO laser

The processes of dissociation and recombination of CO molecules in the plasmas of discharges in He/CO and He/CO/Xe mixtures under conditions characteristic of sealed-off CO lasers are investigated. The concentrations of CO molecules and the main products of their dissociation—O and C atoms and CO2 molecules—are measured simultaneously for the first time, and the time evolution of the initial working mixture composition in the discharge is calculated. It is shown that the main channel for the regeneration of CO molecules in a sealed-off discharge is the heterogeneous recombination of C and O atoms. The rate constants for this process are estimated.

New mechanism for the influence of Xe on the concentration of CO2 molecules in self-sustained CO-laser discharges

The dependence of the CO2 concentration on the discharge conditions and the mixture composition in a CO laser is studied experimentally. The experimental data are compared with the calculated results. A scheme of the reactions that govern the concentration of CO2 molecules under the experimental conditions in question is constructed. It is shown that, in a gas-discharge plasma, an admixture of Xe in a mixture containing CO molecules gives rise to a new mechanism for the dissociation of CO2 molecules by metastable xenon atoms. Under conditions close to the operating conditions of sealed-off CO lasers, the dissociation of CO2 molecules in collisions with metastable. Xe(3P2) atoms becomes the dominant dissociation mechanism in a He: CO mixture because it proceeds at a fast rate. This explains the observed decrease in the CO2 concentration in a xenon-containing He: CO mixture.

Determination of an optimal five-gas combination in a sealed-off CO 2 laser

For obtaining the maximal output power, five lasing gas mixtures (CO2, N2, He, Xe and H2) in a sealed-off CO2 laser are optimized by applying a genetic algorithm and solving CO2 laser kinetics equations. A comparison of numerical simulations shows that the optimal pressures of CO2 and N2 are 1.15 Torr and 7.32 Torr, respectively. Accordingly, the maximum laser power of 124 W is obtained by utilizing the optimal gas combination and an optimized resonator with a length of 1.2 m.

Study on mechanisms for enhancement kinetics of lasing gases in an optimized sea led-off CO2 laser

The kinetics of gases (CO2, N2 and He) in an optimized se aled-off CO2 laser are discussed in details. A comparison of numerical results shows that the po pulation of the laser levels is increased by optimizing the lasing gases, with t he increase of an excited N2 impacting to the upper laser level. Also , decreas ing the electron momentum transition frequency and increasing discharge current result in the increase of the relaxation of the upper rotational laser levels an d the decrease of the level lifetime, thus the lasing saturation intensity in a resonator is increased finally.

Optimization of a sealed-off CO 2 laser resonator by utilizing a genetic algorithm

A genetic algorithm is used to optimize a CO 2 laser resonator. Three optimal parameters of a CO 2 laser resonator (the diameter of the laser discharge tube, the curvature radius of the concave reflector and the transmissivity of the output-mirror) are obtained with the maximum output of the laser power as the objective function in the genetic algorithm. After the optimization, the calculated laser power with the fundamental mode increases by 62% and the measured value increases by 35% in an experiment as compared to a non-optimized case.

Spectroscopic Study of CO2 Decomposition in Sealed-off CO2 Lasers

The CO2 decomposition in a DC glow discharge in a sealed-off CO2 laser mixture (6% CO2 : 20% N2 : 74% He) in the pressure range 2 - 22 Torr is investigated. Both the time evolution and the steady-state CO2 decomposition are studied by means of time resolved optical emission spectroscopy. A decrease of the time to reach steady-state values of particles concentrations in the discharge system with decreasing pressure and increasing discharge current is observed. The degree of CO2 decomposition rapidly decreases with increasing pressure and exhibits only a small increase with increasing discharge current. This behaviour can be explained by the variations of the reduced electrica field strength E/N and of the electron density. Also the influence of the balast volume is discussed in this work.

Sealed-off CO2 lasersexcited by an all-solid-state 0.6 MHz generator

Sealed-off CO2 lasers excited by a dielectric barrierdischarge are studied. The laser output power is measured at excitationfrequencies between 0.3 and 0.6 MHz; discharge gaps are in the range1.6-6.0 mm. The excitation efficiency of the all-solid-state generatorreaches 90%. Due to the scaling laws of radio frequency excitation no laseractivity should be possible for the laser under investigation. The use ofhigh-frequency excitation (0.3-0.6 MHz) combined with a dielectric barrierdischarge gives the possibility of creating a homogeneous stable CO2laser gas discharge with high laser activity. The specific laser power followsthe 1/d scaling law due to gas cooling by diffusion. Even the optimal gaspressure can be increased by high-frequency excitation compared to the radiofrequency excitation.

Dissociation of carbon dioxide in sealed-off CO2 waveguide lasers with radio-frequency excitation

A mathematical model describing the dissociation of carbon dioxide in sealed-off CO2 waveguide and slit lasers with radio-frequency excitation is presented. The theoretically calculated degrees of dissociation of CO2 were tested experimentally. It was demonstrated theoretically and experimentally that the degree of dissociation increases by 5% — 10% with increase in the specific pump power. It was established that the degree of dissociation of carbon dioxide in lasers with the slit design of the discharge channel was approximately 1.5 times higher than in the usual waveguide lasers.

Photoacoustic measurements for catalytic effects of perovskite electrodes in a sealed-off CO2 discharge tube

To investigate catalytic activities of perovskite-type electrodes in a sealed-off CO2 laser cavity, we studied the dissociation and reformation reactions of CO2 during electric discharge by monitoring the concentration change of CO2 as a function of time. A photoacoustic spectroscopy detection was introduced to measure the amount of CO2 in a closed discharge system. The catalytic activities in the dissociation of CO2 were demonstrated and compared for both Cu and La0.7Sr0.3CoO3 cathodes. The discharge with the gas mixture of CO2:N2:He=1:1:8 was performed under nine combinations of different conditions at pressures of 10, 20, and 30 Torr and discharge currents of 3, 4, and 5 mA. Within 1 min after the discharge, the concentration of CO2 reduced drastically by as much as 60% for both cathodes. In the case of the Cu cathode, the amounts of CO2 in the tube had not recovered even after 30 min, while with the perovskite cathode the CO2 contents recovered slowly up to 90%–95% within 5 min and then remained almost unchanged. The dissociation of CO2 with the Cu cathode increased as the total pressure decreased and the discharge current increased. The La0.7Sr0.3CoO3 cathode, however, demonstrated strong suppression in the dissociation of CO2 according to the reformation reaction of CO+(1/2)O2→CO2 by its catalytic activity.

Compact gap single-mode CO2 laser with a hybrid unstable—waveguide cavity

A compact sealed-off metal-ceramic CO2 rf-excite laser with an output power of 30 MW was constructed. The laser is intended for medical and industrial applications. It utilises a discharge structure of the gap type and hybrid unstable—waveguide cavity with propagation of radiation both in free space and in a waveguide.

Enhanced gain and output power of a sealed-off rf-excited CO2 waveguide laser with gold-plated electrodes

The small-signal gain and the laser output power have been measured in a cw sealed-off rf-excited CO2 waveguide laser for two different electrode materials, gold-plated copper and aluminum, at several excitation frequencies, gas pressures and mixture compositions. In the case of the gold-plated electrodes an enhancement of the gain up to a factor of 2 and the output power up to a factor of 1.4 with time at a frequency of 190 MHz and 60 Torr of 1:1:5+5% (CO2:N2:He+Xe) mixture is observed. This is believed to be the result of the gold catalytic activities which are favored by increased electrode temperatures and helium rich gas compositions.

Frequency fidelity of a compact CO_2 Doppler lidar transmitter

The cw, interpulse, and intrapulse frequency stabilities of a compact, sealed-off CO(2) Doppler lidar transmitter are characterized. A cw stability of 1 part in 5 x 10(11) for 1-s averaging times, maximum pulse-to-pulse frequency deviations of +/-49 kHz for periods of seconds at a pulse repetition frequency of 1 kHz, and pulses with low-frequency chirp are demonstrated in a instrument suitable for the field.

Use of zeolites for the stabilization of CO2 partial pressure in sealed-off CO2 waveguide lasers

A new method to stabilize the CO2 concentration in sealed-off CO2 lasers is presented. Molecular sieves (zeolites) are used to adsorb large amounts of CO2, allowing compensation of losses of CO2 arising mainly from oxidation processes, other chemical reactions and O2 adsorption. The adsorption process of CO2 and water vapour in zeolites is theoretically described using Langmuir's isothermic equation. The theory allows a determination of the optimum quantity of zeolite and gives a temperature dependence of the adsorptive capacity. A RF-pumped CO2 waveguide laser is used to test the CO2 pressure stabilization. The measurements were performed by means of a quadrupole mass spectrometer.

Effects of H2 and CO Additives on the O2 Accumulation in the TEA CO2 Laser

A change in gas mixture in a sealed-off TEA CO2 laser discharge was analyzed gas-chromatographically. It has been found that the addition of a small amount of H2 and CO will reduce the O2 formation in the mixture. In particular, when a mixture of N2:CO2:CO:H2:He=12:12:6:1.6:68.4% was used, a sealed-operation lifetime exceeding 5 × 105 shots without any oxygen formation was obtained. However, it has also been found that CO2 was decomposed by discharge and formed O2 was missing. No nitrogen oxide formation was recognized, implying that the missing oxygen was dissipated to some other reactions. Furthermore, notable differences in the change in the electrode surface, with addition of CO or H2 to the mixture, were recognized by visual observation. Hence, we proposed electrode surface reactions for the reduction in the O2 formation in the mixture.

Frequency tuned carbon monoxide waveguide laser with rf pumping

The results of the investigation of a rf-discharge-excited sealed-off CO waveguide laser with a selective resonator are reported. The operation on more than 40 vibration-rotation transitions of a CO molecule has been obtained in a laser having a square section (Al/BeO) waveguide with dimensions of 1.5×1.5×180 mm. Maximum frequency tuning of 550 MHz with output power of 0.5 W at line centre has been observed on theP10−9(17) transition at −20°C ground electrode temperature at a pressure of 180 Torr.

The effect of C13O162 on the performance of a sealed-off pulsed CO2 laser

A sealed-off rf-excited CO2 waveguide laser was used to investigate the relative performance with C13O2 and C12O2 mixtures. By modulating the laser at various rates and pulse widths, we demonstrated effects due to both temperature and upper level relaxation rates. In addition, replacing N142 with N152 was shown to improve the performance of C13O2.