Sealed-off CO2 Lasers Research Articles

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.

密封式CO2激光谐振腔的设计

密封式CO₂激光谐振腔的设计

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.

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.

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.

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.

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.

Oxide conductive coated cathodes for a sealed-off CO2 laser

Cold cathodes coated with oxide conductive materials, such as indium tin oxide and tin oxide, were applied to dc gas discharges of a sealed-off CO2 laser. Laser power enhancement and stable gas discharge, two areas of laser performance, were affected, in contrast to the uncoated metallic cathode. Mass spectrometric study revealed a correlation of laser power enhancement and an increase in the CO2 content associated with these coated cathodes.

Estimation of Small Signal Gain and Saturation Intensity in a Waveguide CO2 Laser by a Curve-Fitting Technique

Output power curves as a function of the frequency have been measured by heterodying between a gas flowing waveguide and a conventional sealed-off CO2 laser with a W–Ni point contact diode. The small signal gain, saturation intensity, collision-broadened linewidth and frequency tunability are simultaneously estimated by fitting a theoretical equation to output power curves according to a least-squares technique.

Lifetime improvement of a visible multiline CO laser

The influence of charge capacitance, tube bore, and oxygen addition on the lifetime of a sealed-off visible carbon monoxide pulsed laser is reported. The results extend previous studies on the CW IR sealed-off CO laser.

Sealed-off CO2 laser with In–Au alloy sealing

The In–Au alloy sealing was found to satisfy all the requirements imposed on the sealed-off CO2 lasers. The sealing between different materials such as quartz, SUS 303, Si, and ZnSe was shown to withstand the thermal shock test, and gave the He leak rate lower than 1×10−9 atm cc/s both before and after the tests. It was also proved that the transmittance characteristics of dielectric coated output couplers did not change after the sealing. The sealed-off CO2 lasers with La1−xSrxCoO3 perovskite oxide cathodes sealed with this technique produced the operational life of 3000 h at the laser power level of 50 W/m.

The effect of He3 on CO2 laser power

Substitution of He3 for normal helium in a sealed-off conventional CO2 laser resulted in power output increases as high as 14%. No such effect was observed in a narrow-bore waveguide laser, indicating that the observed improvements were due to more efficient heat conduction to the tube wall.

Sealing Characteristics of Optical Component for Sealed-off CO<SUB>2</SUB> Lasers

An In-Au alloy sealing was found to satisfy all the requirements imposed on the developing a sealed-off CO2 laser which has long life and high reliability. The sealing between different materials such as quartz, SUS303, Si and Zn Se was shown to withstand the thermal shock test, and gave the He leak rate lower than 1×10-9 atm-cc/sec both before and after the tests. The value of it could guarantee the shelf life of the laser tube for longer than 10 years. It was also proved that the transmittance characteristics of dielectric coated output couplers did not change after the sealing process. The sealed-off CO2 lasers with La1-xSrxCo O3 perovskite oxide cathodes sealed with this method turned out the operational life of 3000 hours at the power level of 50 W/m.