Sealed-off CO Research Articles

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.

Novel technology and performance of a high-power CO 2 waveguide laser

Several new techniques have been developed to solve the problems encountered in the design and construction of rugged, reliable, high-power, CO 2 waveguide lasers. High-power single transverse mode output requires long single- or multiple-folded waveguide paths to be created in a dense ceramic body. The limitations of extruded or drilled bores have been overcome by fabricating the waveguide in two halves which are subsequently bonded together with a glaze or by thermodiffusion to form a vacuum-tight assembly. Several lasers have been constructed by these methods, one such device giving over 10 W CW output is described. These techniques can be readily extended to larger, higher-power devices. Reliable seals between semiconductor optics and metals using pure In soldering have also been developed for clean “hard seal” assembly. Dissociation of the CO 2 gas can lead to rapid decline in output power. The effects can be reduced by attaching a reservoir to the laser, or more preferably by the incorporation of a catalyst to reverse the reaction. These techniques have been applied to sealed-off CO 2 waveguide lasers which have demonstrated 5 yr shelf life and up to 5000 h operating life.

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.

Control of OH catalyst in a CO2 laser via NbHx-H2 equilibrium

The partial pressure of H2 in a sealed-off CO2 laser was controlled by changing the temperature of a Pd-plated NbHx specimen placed in the laser tube. It was shown that the pressure control could be performed uniquely even in the presence of H2 adsorption or outgassing, provided the quantity of Nb exceeded a certain amount. Controlling the H2 pressure led to varying the concentration of OH radicals in the CO2 laser plasma, the catalytic activity of which was monitored as the change of laser output power.

Power Enhancement of Sealed-off CO2 Lasers by Incorporating Catalysts

Various catalysts were tested and evaluated for enhancing the output power of sealed-off CO2 lasers by suppressing the CO2 dissociation in the discharge tube. They include (i) two kinds of distributed heterogenous catalysts, i. e. sputtered Pt layer and ion-exchanged Pt on MnO2 layer both on the internal surface of laser tube, (ii) homogeneous H2 catalyst generated from the equilibrium dissociation of Nb Hx and finally (iii) catalytic cathode made of La1-xSrx CO3 perovskite oxide.Among them, the La0.7 Sr0.3 CO3 cathode sintered at 1150°C acted satisfactorily producing the output power of 52W/m, which was almost equal to that of a gas flowing laser. The longest life of this laser was 4400h at the discharge current of 15mA. This excellent performance resulted from the simultaneous presence of metallic conductivity, catalytic activity, oxygen emissivity and low sputtering rate in the perovskite cathode material.

Sealed-off CO2 lasers with La1−xSrxCoO3 oxide cathodes

Some of the perovskite oxides such as La0.7Sr0.3CoO3 sintered at 1150 °C can have the function, when used as cathode materials in sealed-off CO2 lasers, to improve both output power and operating life. While the output power of the order of 50 W/m has become obtainable in sealed-off tubes, the longest life observed was 4400 h. It has been shown that this improvement comes from the simultaneous presence of the following properties in some perovskites, of oxygen emissivity, catalytic activity, metallic conductivity, and low sputtering rate.

Tunable sealed-off CW CO laser at room temperature

Starting from a sealed-off CO laser with a long-life output of 29 W/m in multiline operation, we developed a tunable version of this device. The system described has a discharge length of 97 cm. It was made transition-selective by using a three-mirror configuration. In this way we were able to tune the laser to more than 70 oscillating vibrational-rotational transitions of the CO molecule.

Status of CO<inf>2</inf>isotope lasers and their applications in tunable laser spectroscopy

The use of CO 2 isotopes can provide a manifold expansion of the usable frequency range of sealed-off CO 2 lasers. Determination of the frequency, gain, and saturation parameter of the various CO 2 isotopic laser transitions will be discussed. Design considerations for constructing CO 2 isotopic lasers and selected applications will be presented.

Small signal gain and saturation intensity of 00° 1-[10°0, 02°0]<inf>I and II</inf>vibrational band transitions in sealed-off CO<inf>2</inf>isotope lasers

Effects due to Fermi resonance play a major role in determining the very significant variations of gain in the various CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> isotopes. We have measured the small signal gain coefficients and saturation parameters for five transitions ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J= 12, 16, 20, 24, 28</tex> ) in each of the four rotational branches of the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">00\deg 1-[10\deg0, 02\deg0]</tex> <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I and II</inf> vibrational bands using sealed-off TEM <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ooq</inf> mode oscillators and amplifiers. Isotopic species of pure <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> C <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">16</sup> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> , <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> C <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">18</sup> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> , <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sup> C <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">16</sup> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> , <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sup> C <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">18</sup> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> , and <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sup> C <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">16</sup> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> were measured with <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> He- <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sup> N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> -Xe gas additives under identical conditions. Substitutions of either <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</sup> N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> or <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sup> C <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">16</sup> O instead of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sup> N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> were also tried. The results obtained may serve as guidelines in the design of sealed-off CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> lasers and amplifiers.

Efficient simple sealed-off CO laser at room temperature

A sealed-off cw CO laser with gold electrodes is described. With this simple device we measured a constant, long-life output power of more than 29 W/m and a maximum efficiency of 15% at room temperature. No auxiliary features, such as a palladium hydrogen extraction tube, are necessary.

Efficient self-sustained pulsed CO laser

In this paper a simple sealed-off TEA CO laser is described with a self-sustained discharge without an external UV preionization source. At 77 K this system yields more than 600 mJ from a lasing volume of about 60 cm 3 CO-N 2-He mixture (45 J/ℓ atm. with 15.6% efficiency).

Pulsed CO_2 TEA laser rangefinder

A compact laser rangefinder has been developed, which incorporates a sealed-off pulsed CO(2) TEA laser and uses direct (i.e., nonheterodyne) detection. This device is essentially eye safe and benefits from the superior atmospheric transmission at 10.6-microm wavelength. Design parameters are presented and illustrated, and system performance is discussed.

Gain induced stability of active plane-parallel resonators

It has been observed for a plane-parallel resonator with a saturated medium that under certain conditions confined beams mainly concentrated near the axis are present. The experiments have been done with a sealed-off plane-parallel CO2 laser of one meter length and with an internal diameter of 20 mm. Without gain variations such a system is unstable because of thermal defocussing by the heated gas. But due to sufficiently high gain variations the beam converges nevertheless. Since the gain variation increases with decreasing reflectivity confined beams near the optical axis are only observed at sufficiently low reflectivity. The experiments were done with a totally reflecting mirror and an outcoupling mirror having a reflectivity of, respectively, 90%, 80%, 50%, and 36%. For the high reflectivities the outcoupled beam is mainly concentrated near the edge with irregular density distributions. For the low reflectivity the beam is more or less radially symmetric, concentrated near the axis having decreasing intensity with the distance from the axis. The behaviour can be understood by an analysis in which the constant and quadratic term of the complex propagation constant near the optical axis due to gain variations, dispersion and heat effects are taken into account.

Airborne Laser Doppler Velocimeter

A CO(2) laser Doppler detection system has been developed to measure remotely the true airspeed of an aircraft. The system uses a 50-W sealed-off CO(2) laser in a homodyne detection system employing a collinear optical telescope, a HgCdTe detector, and a frequency tracking loop. The system was successfully flight tested on a NASA Convair 990 research aircraft during December 1971 and June 1972. The results indicate that an airspeed measurement under clear weather conditions is feasible up to an altitude of 3000 m with an error of less than 0.5%.

Gain induced stability of active plane-parallel resonators

It has been observed for a plane-parallel resonator with a saturated medium that under certain conditions confined beams mainly concentrated near the axis are present. The experiments have been done with a sealed-off plane-parallel CO2 laser of one meter length and with an internal diameter of 20 mm. Without gain variations such a system is unstable because of thermal defocussing by the heated gas. But due to sufficiently high gain variations the beam converges nevertheless. Since the gain variation increases with decreasing reflectivity confined beams near the optical axis are only observed at sufficiently low reflectivity. The experiments were done with a totally reflecting mirror and an outcoupling mirror having a reflectivity of, respectively, 90%, 80%, 50%, and 36%. For the high reflectivities the outcoupled beam is mainly concentrated near the edge with irregular density distributions. For the low reflectivity the beam is more or less radially symmetric, concentrated near the axis having decreasing intensity with the distance from the axis. The behaviour can be understood by an analysis in which the constant and quadratic term of the complex propagation constant near the optical axis due to gain variations, dispersion and heat effects are taken into account.

Cold cathodes for sealed-off CO&amp;lt;inf&amp;gt;2&amp;lt;/inf&amp;gt;lasers

Cold cathodes for CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> lasers should possess a very low sputtering rate, have a minimum of negative ions in the sputtering products, and consume no oxygen. These conditions can be satisfied by selecting cathode materials from those elements of group I in the periodic table which form semiconducting oxide layers and then exposing these elements to a reducing gas mixture. Experimental results show that silver, internally oxidized silver-copper alloys, and pure copper satisfy most of these requirements in He-CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> -CO-Xe gas mixtures. Infrared CO and CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> gas analysis performed on simple gas discharge tubes using such cathodes indicate that laser lives of 10 000 h can be expected. In our laboratory a 1-W sealed-off CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> laser using a gas volume of only 50 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> had an initial power output of 0.72 W which rose to 1.1 W after 3000 h and still gave 0.7 W after 12 000 hours; the laser used an internally oxidized silver-copper alloy cathode.