Far infrared frequency synthesis with stabilized CO2lasers: Accurate measurements of the water vapor and methyl alcohol laser frequencies

A far infrared (FIR) frequency synthesis technique using saturated-absorption stabilized CO2lasers and a point-contact diode has been used to measure frequencies of a number of strong CW H2O, D2O, and CH3OH laser lines. The first frequency measurements of the 79-μm H2O, the 73- and 108-μm D2O, and 11 CO2-pumped CW¹²CH2¹⁶OH laser lines are reported. This measurement is the first demonstration of the general usefulness of CO2lasers for accurate synthesis of FIR frequencies.     

Reaction property of diffused H2with defect Centers in GeO2-doped fiber

This paper presents the reaction property of diffused molecular hydrogen (H2) with irradiation-induced defect centers in a GeO2-doped fiber. When H2diffuses into an irradiated fiber, an OH loss increases even at room temperature. This loss increase is thought to be caused by chemical reaction between diffused H2and irradiation-induced nonbridging oxygen hole centers (NBOHC's). The hydrogen-associated defect centers having 11.9-mT hyperfine structure are formed by chemical reaction between diffused H2and irradiation-induced Ge-defect centers. Moreover, the irradiated fiber shows an OH loss increase at high temperatures even after diffused H2is removed from the fiber. The hydrogen-associated defect centers are considered to be the hydrogen source for the OH formation.     

Transition metal-gate MOS gaseous detectors

MOS capacitors with gates of palladium, platinum, and nickel are shown to be sensitive detectors of H2, CH4, C4H10, and CO gases. 1-MHz and 10-HzC-Vcharacteristics change by - 1240 and - 215 mV when the Pd-gate MOS capacitor is exposed to H2gas at 760 and 2 × 10^-8torr, respectively. Platinum-gate MOS capacitors exhibit approximately one-half the change of Pd-gate devices. Nickel shows a response of - 120 and - 140 mV in 1 atm of H2find CO gas, respectively. When the capacitors are operated in a constant-capacitance mode by varying the bias, absorption time characteristics are obtained. Pd-gate devices absorb H2gas in 190-200 ms at 760 torr of H2but require 200 min to reach 63 percent of the total change at 2 × 10^-8torr H2pressure. Both Pt- and Ni-gate devices are slower than Pd. The detection mechanism is attributed to the change in work function upon hydrogen absorption. This is established by demonstrating no change either in the density of interface states or in the distribution across the gap or in the number of states at midgap upon absorption. Also, no accumulation of additional charges in the SiO2or Si3N4dielectric is found upon hydrogenation of devices with either Pd or Pt gates.     

A study of Pd/Si MIS Schottky barrier diode hydrogen detector

Pd/Si MIS Schottky diode hydrogen detectors have been fabricated with a response of 2-3 orders of magnitude change in current for 154 ppm of H2in N2. Detailed evaluation of dark I-V, C-V, illuminated I-V, and internal photoemission data unambiguously ascribes the strong hydrogen sensitivity of these diodes to hydrogen-induced change in the work function of Pd, rather than to any surface-state effects. The reaction rate of the device to different gas ambients has been studied with time response measurements. A long-term degradation mechanism has been identified and traced to the poisoning of Pd by environmental sulfur. The role of oxygen and atomic hydrogen in determining the Schottky barrier height also is discussed in some detail.     

Time-resolved output spectrum from a hydrogen fluoride laser using mixtures of SF6and HI

The time-resolved spectrum from a transverse-discharge hydrogen fluoride (HF) laser using a mixture of SF6and HI is reported. Because this spectrum matches that from a high-pressure H2- F2laser, and because the SF2-HI mixture is chemically stable, this laser should be a suitable and convenient source for probing H2- F2amplifiers.     

Thick-film CO gas sensors

A gas sensor of SnO2-based materials has been made by thick-film technology utilizing hydrophobic silica as a binder. The technology can achieve a high productivity as well as a reduced humidity dependence and a sufficient mechanical strength of sensors. A thick-film sensor of SnO2incorporated with ThO2shows highly selective detection for CO gas, separated from H2gas; i.e., sensitivity to CO is 42 times higher than to H2at both gas concentrations of 50 ppm. An excellent humidity-independent sensitivity is also achieved.     

High repetition rate pulsed gas lasers and their applications in chemistry and isotope separation

Presented in this paper are the results of experimental studies of pulsed high repetition rate XeCl, CO2, NH3, and CF4lasers with a closed gas cycle. Some applications of these lasers in chemistry and isotope separation are discussed.     

Performance of an HF chain-reaction laser with high initiation efficiency

Output-pulse observations are presented for a tranverse electrically initiated, helium-diluted HF laser pumped by the H2+ F2chain reaction. Performance of this laser is studied over a wide range of the gas composition and for initial pressures between 0.1 and 0.5 atm. The gas mixture was stabilized by premixing O2, F2, and He and flowing this mixture into a cold trap (84 K) before mixing with H2. Optimum conversion of electrical-initiation energy into laser energy was found for a 240-torr mixture with a mole ratio 1 F2:0.23 H2:0.08 O2:12 He which, when initiated with a 25-kV, 333-pF discharge, gave a pulse energy of 0.150 J. This corresponds to a ratio of laser output energy to electrical input energy of 144 percent. After unnecessary losses are taken into account, this ratio becomes 160 percent.     

Life and parameter studies on sealed CO2lasers

The life and power outputs of sealed CO2lasers with xenon and hydrogen additives have been investigated. The results confirm the usefulness of hydrogen for achieving long life, but suggest that the power increases previously observed with the addition of hydrogen may be due to changes in CO2concentration rather than to relaxation effects.     

A sealed high-repetition-rate TEA CO2laser

A compact atmospheric pressure CO2laser utilizing a double-discharge technique has been constructed and operated at repetition rates to 100 pulses/s. With the addition of small amounts of hydrogen and carbon monoxide to give a gas mixture of He:N2: CO2:CO:H2= 69.3:11:15:4:0.7, sealed operational lifetimes exceeding2 times 10^{6}pulses have been obtained. Operating in this mode, the output energy density is about 8-9 J/l at repetition frequencies of 30-40 pulses/s for input energy densities of 60-70 J/l. The operation of the sealed laser has been studied by means of mass spectroscopic measurements of the gas mixture. It has been determined that sealed operation is possible as long as the oxygen concentration is kept below 1-2 percent. It has also been found that the addition of small amounts of H2and CO will keep the oxygen concentration below 2 percent by reducing the CO2decomposition, allowing sealed operation. The experimental results are compared to the predictions of a theoretical model in which neutral and negative-ion processes have been included. The calculations indicate that when small amounts of oxygen or water are present in the discharge the negative-ion population is significantly increased and the ratio of negative-ions to electronsN_{n}/N_{e}can approach values near unity. These are the conditions under which discharge arcing was found to occur. The model also predicts that the dissociation equilibrium of the CO2can be controlled by the addition of the above concentrations of hydrogen and CO.     

Stimulated vibrational Raman scattering in HD

This letter reports an observation of stimulated vibrational Raman scattering in HD gas. The Raman threshold data are compared to those of H2under similar conditions, and the difference in their gain coefficients is discussed.     

Characteristics of sealed-off waveguide CO2lasers

Gain and output power of sealed-off waveguide CO2lasers are presented as a function of gas mixtures and total gas pressure. Experimental data on circular-bore and square-channel waveguide lasers are presented. Output power per unit length of 0.2 W/cm is achieved for both types of lasers in agreement with gas-discharge scaling laws which are presented. Saturation intensities as high as 24 kW/cm²are inferred from the data. The effects of the optical properties of the waveguide wall material on the waveguide losses are discussed and theoretical waveguide loss versus wavelength is presented for BeO, Al2O3, and fused silica.     

Glass envelope UV-sensitive flame detectors

The need for fast-response low-voltage flame sensors, able to operate for long periods in ambients presenting a wide range of temperatures, prompted the construction and testing of gas amplification UV-photosensitive detectors utilizing 9741 glass envelopes and a variety of gas fills and electrode and getter materials. Addition of 1 mole percent H2to a He gas fill reduced the required minimum time between counts for a given sensor operating voltage without significantly changing the threshold voltage. All sensors with H2additive ultimately became solar sensitive. Sensors performed well at temperatures as high as 350°C.     

Submicrosecond pulses from a hydrogen-fluorine laser with high energy density and quantum efficiency

Submicrosecond pulses have been obtained from a photochemical H2-F2laser with a chemical efficiency of 0.5 percent. Energy densities of 6 J l^-1were obtained from 60 torr (at 213 K) of a stoichiometric H2-F2mixture stabilized with 5 mole-percent O2. Laser output energy and the reciprocal of the pulsewidth were both proportional to the gas pressure. Actinometry showed that the laser energy output was 16.6 times the energy necessary to provide F atoms for initiation. Time-resolved spectra revealed excitation up toupsilon' = 6.     

Gamma-ray radiation effects on hydroxyl absorption increase in optical fibers

This paper presents gamma-ray irradiation effects on OH-loss increase due to the chemical reaction of H2for GeO2-doped and GeO2. P2O5-doped fibers. When H2diffuses into irradiated fibers (γ-H2treatment), OH-loss increase occurs even at room temperature. Moreover, OH-loss increases due to dissolved H2in irradiated fibers are larger than those in unirradiated fibers at high temperatures. These OH-loss increases are attributed to irradiation-induced defects with which H2reacts to form OH ions. When H2-dissolved fibers are irradiated, the OH-loss increases are larger than those in the γ-H2-treated fibers at room temperature. These larger loss increases are thought to be caused by the reaction of the unstable radical and dissolved H2, which are excited by the irradiation.     

A dual-mechanism solid-state carbon-monoxide and hydrogen sensor utilizing an ultrathin layer of palladium

Pd-gate MOS sensors were fabricated on p-type silicon wafers. The gate films were 25 and 40 Å thick with an oxide thickness of 100 Å. Contacts were made to allow measurement of the MOS capacitance and of the impedance across the gate film. Voltage shifts in the MOS C-V curves and shifts in the Pd film impedance were measured as functions of 1) the concentration of CO and H2; 2) time as the gas ambient was varied. The devices showed sensitivity to H2at room temperature and to CO and H2at elevated temperatures. When the 25-Å device was exposed to 300 ppm H2in air at room temperature, the C-V curve shifted by -430 mV and the impedance decreased by 20 ω or 5 percent. When the 25-Å device was exposed to 5000 ppm CO in air at 150°C, the C-V curve shifted - 200 mV and the impedance decreased by 140 ω (10 percent). When exposed to 0.1-percent H2in argon, the resistance of the 40-Å device increased by about 2 percent. When measured as a function of time, the changes in MOS capacitance tend to track the changes in impedance. An effect similar to hydrogen-induced drift (HID) was observed for CO at elevated temperature.     

Laser cleanup of H2S from synthesis gas

Hydrogen sulfide at the 10 ppm level has been selectively stripped from a CO + H2synthesis gas by photolysis with an ArF laser. The sulfur in the atomic or radical form is irreversibly removed by a metal surface. Spectroscopic and quantum yield data are presented. An H2S spectroscopic selectivity less than 10⁷was measured in the 210-220 nm range, a wavelength range compatible with Raman-shifted ArF or KrF lasers. The laser purification method described here is a potential approach to achieve sulfur impurity levels greater than 0.1 ppm. This method is of potential industrial significance for extending the lifetime of syngas metal catalysts.     

Role of helium in TEA CO2lasers

The role of helium in TEA CO2lasers differs from that in low-pressure CO2lasers. TE CO2laser output is nearly proportional to the gain-bandwidth product, and, at a total pressure of 250 torr, it is independent of whether helium is present or not. Above 250 torr, the laser could not be operated without helium.     

Gain characteristics of CO2laser amplifiers at 10.6 microns

Single-pass gain at 10.6 microns has been studied parametrically in nonflowing CO2or buffered CO2amplifying media. The gain profile across the amplifier diameter and integrated gain both were determined. Parameters varied included buffer gas type, mixture ratio, gas pressure, amplifier bore, discharge current, and wall temperature. Tube bores of 12, 22, and 34 mm and buffer gases of H2, He, Ne, A, and N2were studied. Optimum gain is relatively independent of current density, but decreases with increasing wall temperature. The pressure-diameter relationshipP_{CO_{2}} cdot D sim 4torr-cm was found to hold for CO2, CO2:He, and CO2:N2amplifying media at optimum gain. The gain depends strongly on the CO2partial pressure and is relatively insensitive to the buffer gas pressure except for the case of H2. The maximum gain decreased slowly with increasing amplifier diameter. The highest gain, 1.7 dB/meter, was achieved with a helium buffer gas in amplifiers with a diameter of 22 mm or less. No gain saturation was detected for a 30-dB range of input signal power, from a milliwatt to a few watts. Spectrograms showed that the principal spontaneous emission from CO2:He amplifiers in the 2000-7000-Å range consisted of CO bands; no CO2bands or He line spectra were observed.