The microwave absorption by H2O vapor and its mixtures with other gases between 100 and 300 Gc/s

The microwave absorption between 100 and 300 Gc/s by H2O vapor and its mixtures with N2, CO2, and O2has been measured at room temperature for intermediate and atmospheric pressures. Near the absorption lines the line shape parameters are close to those measured at low pressures by Rusk. Between the lines, very large absorption coefficients were observed, particularly for self-broadening and for broadening by CO2. This increased absorption is ascribed to collision-induced polarization of the molecules involved. Empirical formulas are given for the calculation of line shapes. These formulas require the use of four line-shape parameters for each mixture--two of these are for the line centers, the other two for the wings.     

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.     

Mass spectroscopic studies of the CO laser discharge

The effects of adding Xe, H2, and O2to the CO-He laser discharge are studied mass spectroscopically. Xe greatly reduces CO dissociation. H2does not react chemically but alters discharge kinetics. O2has little effect on the CO-Xe-He discharge but reduces CO dissociation in CO-He.     

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.     

Study of electron emitters for use in gas lasers

This paper describes various types of electron emitters that have been tested under conditions of interest in gas laser operations. In general, where "nonreactive" gases are used, some form of the BaSrO cathode will meet many requirements. Several matrix structures containing BaSrO are described that will stand up better under adverse conditions (ion bombardment, envelope poisoning) than the conventional sprayed cathode. Several hot hollow cathodes for use at high (15-100 amperes) currents were studied and are discussed. With reactive gases, such as O2, CO2, H2O, a BaZrO3cathode has been found to be very useful. This cathode is unique in that it emits better in an oxidizing atmosphere than it does in either an inert gas or vacuum.     

Simultaneous HCN and H2O laser emission in mixtures containing H, C, N, and O

Simultaneous laser emission at 337 and 118 μ has been observed in a pulsed discharge through a mixture of N2, O2, and either CH4or (C2H5)2O. Earlier observation of a laser line at 469 μ is rejected and explained.     

Laser action from atmospheric-pressure H2-F2mixtures made at 300K

Thirty-five photons (lambda = 3 mum) per photolytic F atom have been obtained from a 40-cm³photochemical laser filled with 400 torr of F2, 100 torr of H2, and minor amounts of Ar and O2mixed at 300 K. With 0.035-percent dissociation of the F2, 0.83-J 250-ns full width at half maximum (FWHM) pulses were observed.     

The F + H2O chemical laser

Laser oscillation, restricted by energy limitations to transitions from first vibrationallevel to ground state, has been observed from HF produced by the reaction of the F atom on H2O initiated by pulsed electric discharge in flowing mixed F2-H20-He gases at 10 torr.     

Gas additive effects in CO chemical lasers

The effects of gas additives on optical gain of the CO chemical laser (CL) have been measured for N2, SO2, H2, HF, CF4, CCl2F2, CO, OCS, N2O, and NO. One of the more unusual additives, NO, has been used to control the output spectrum of a laser oscillator by controlled sequential quenching of the high bands. The significance of these results for total power enhancement, output spectrum control, and alternate diluent use is discussed.     

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.     

A study of the CW 28-µm water-vapor laser

The low signal gain of a CW water-vapor laser at 28 μm was measured as a function of the discharge current and pressure. Together with the measurement of other quantities such as the axial electric field and the concentration of OH, a partial interpretation of the mechanisms involved in pumping the 28-μm transition was possible. Thermal equilibrium between the ν0,2nu_{2}, and ν3vibrational levels will result in a large absorption at the elevated gas temperatures observed (800-1000 K). The strong dependence of gain on the electron temperature strongly suggests that the vibrational excitation proceeds through electron-impact excitation. Only the electron-impact excitation of H2O is quantitatively capable of overcoming the large thermally induced absorption. Although vibrational-excitation transfer from H2to H2O seems insufficient, by itself, to overcome this absorption, it may provide appreciable additional gain. Pumping of the 28-μm line through electron-ion recombination and by reactions involving OH can be ruled out.     

Near single-line operation of a free-burning CS2/O2/N2O flame laser with a nondispersive optical cavity

The CS2/O2/N2O flame laser has been operated for the first time under conditions in which the spectral output is nearly single line. This transition is theP_{10-9}(17) of CO at 5.4265 μm, the same transition which was observed to oscillate in single-line fashion by Hirose et al. in an electrically initiated CO chemical laser. It is suggested that the unique behavior of this line may be due to its close proximity to aPbranch transition in an adjacent band, namely theP_{9-8}(23) line, such that the gain profiles of the two lines overlap. Calculations suggest that at the conditions of these experiments, the separation of the line centers for this pair is about 0.3 Å or less. TheP_{10-9}(17) transition was also found to be totally absent under certain conditions of high multiline power, particulary at low O2and N2O flows. This may be due to absorption by a high-bandRbranch transition at 5.4266 μm, namely theR_{15-16}(32) line.     

Efficient ultraviolet generation of 2073-2174 Å in KB5O8/4H2O

Efficient generation of tunable UV radiation at 2073- 2174 Å has been achieved by Type-1 frequency mixing of the fundamental and second harmonic of a high-power visible dye laser in KB5O8/4H2O. A peak power as high as 250 kW with an average power of 15 mW was obtained at 2073 Å.     

Vibrational energy transfer in CO2under laser conditions with and without water vapor

It is shown that in the case of a dry 1.5-torr CO2gas fill the upper laser level is indirectly excited by vibrationally excited CO produced during the discharge, whereas in the case of a 1.5-torr CO2and 0.2-torr H2O mixture the upper laser level is directly excited by the electrons in the discharge. The collision relaxation times measured under laser conditions for the symmetric valence vibration of CO2in a CO2-H2O mixture and in a CO2-CO mixture as produced during a discharge of an initially pure CO2fill were 19 and 73 μs, respectively. If the reasonable assumption was taken that half of the CO2was dissociated into CO then this result shows that H2O was 14 times more effective in depopulating the lower laser level than CO. The growth in laser intensity for the dry fill was shown to be due to the CO (nu = 1) transfer of energy to the asymmetric vibration of CO2(00°1) with a characteristic increase that was exponential strictly only for a time short compared with the relaxation time of the symmetric vibration. The characteristic transfer time for excitation of the asymmetric vibration was dependent upon the fraction of CO present. If we make the assumption of 50 percent dissociation, the intermolecular energy transfer time between CO and CO2was found to be 40 torr-μs. Results obtained with N2and He added to the laser mixture indicated that He was not more effective in relaxing the lower laser level than N2or CO and was less effective than H2O.     

Far-infrared laser emission in gas discharges containing boron trihalides

Laser emission has been observed at 54 wavelengths between 11 and 41 μ in pulsed electrical discharges in BF3, BCl3, and BBr3. The emission wavelengths have been measured and the time behavior of the lines studied. Lasing in each of the gases produces total peak powers on the order of 10 to 100 mW. The addition of N2, He, or H2O to the discharge is found to have considerable effect on the peak powers of various lines and on the total energy emitted. The observed wavelengths are consistent with pure rotational transitions in HF, HCl, and HBr. Some short wavelength lines in the1.5-6 muregion are also observed but do not appear to be associated directly with the far-infrared emissions.     

Gain and fluorescence characteristics of flowing CO2laser systems

Single-pass gain has been measured for flowing CO2, CO2-N2, CO2-He, CO2-N2-He, and CO2-N2-H2mixes. The gain for CO2-N2mixes varies as d^-0.9, wheredis the tube diameter. The diameter dependence of the gain is less pronounced for CO2- N2-He mixes; a peak gain of 4.7 dB/m was obtained in a 1/2 in diam tube. Fluorescence data indicate that the upper laser level population is saturated at 100 mA in all cases. The addition of He, H2, or O2depopulates the lower laser level; helium further increases the population of the upper laser level. The addition of CO increases the population of the upper laser level, probably by resonant transfer from the excited vibrational states of CO.     

HF and DF laser action by a pulsed microwave discharge

A pulsed electrodeless microwave discharge withE-field enhancement by a tapered waveguide has been employed to produce HF and DF laser radiation from premixtutes of SF6+ H6and SF6+ D2. The 720 patm (690 patm) HF (DF) laser had an average multiline output power of 6 mW (1 mW) for an efficiency of 0.1 percent (0.02 percent) while operating at 1 kHz (450 Hz) pulse-repetition frequency (PRF). The HF (DF) laser was operated at reduced output power and efficiency up to 4.2 kHz (2.5 kHz) PRF. Reduced HF laser efficiency was obtained when C3H8was substituted for H2.     

Relaxation of CO2laser levels by collisions with foreign gases

Relaxation time of the 00⁰1 upper and 10⁰0 lower CO2laser levels as a function of H2O, CO, and Xe gas pressure has been measured using the afterglow pulse-gain technique. Lifetime data for these gas mixtures and also for mixtures of CO2, CO2-H2, CO2-He, and CO2-N2, obtained previously, are analyzed and compared with available ultrasonic and fluorescence data. Results indicate that the 10⁰0 and 01¹0 levels of CO2are strongly coupled and depletion of the lower laser level population is essentially limited by the relaxation rate of the 01¹0 level. Other processes involving energy exchange between CO2and foreign gases are detailed.     

A new tungsten gate process for VLSI applications

In spite of the growing demand for MOS gates and interconnections of higher conductivity, the refractory metal gate process has not received as much attention as those using silicides because it is incompatible with the Si-gate process. The metal gate cannot withstand oxidizing annealing ambients, and source-drain formation by ion implantation is difficult because of the channeling of doping ions through the gate metal during ion implantation. In a new process developed for use in MOS VLSI fabrication, tungsten (W) is used as a gate metal because degradation of SiO2by annealing the metal/SiO2/Si structure at around 1000°C can be minimized if the metal is W. Metal oxidation is prevented by using a H2/H2O ambient for this annealing, which also allows Si to be oxidized in the same ambient. The channeling mentioned above is stopped by forming a thin layer of PSG or WOxon the W. This gate process is believed to be a step forward toward the desired compatibility.     

Prediction of new optically pumped submillimeter-wave laser lines in deuterated fluoroform

Over 300 new submillimeter-wave laser emission lines are predicted for the ν5band of deuterated fluoroform (CDF3) when isotopic CO2and N2O infrared pump lasers are used. These lines are calculated by using recently derived molecular constants that were determined by fitting known infrared, microwave, and submillimeter-wave transitions in CDF3. The calculated emissions (estimated accuracy generally within ± 1 MHz) should be useful to those with specific wavelength requirements. The molecule provides a rich choice of frequencies at approximately 20 GHz intervals extending from about 40 GHz to beyond 1 THz. This approach eliminates much of the usual trial-and-error technique of finding new submillimeter-wave emission lines.