A CRADA was established in 1991 to study the production and mitigation of S{sub 2}F{sub 10}, one of a number of toxic by-products formed by electrical discharges in the insulating gas SF{sub 6}. Since compressed SF{sub 6} is extensively used as an insulation and current interruption medium in electric power equipment, ensuring the safe operation and maintenance of this equipment is an important issue for utilities, government agencies, and manufacturers. Each of the three research laboratories developed a highly sensitive detection method for S{sub 2}F{sub 10}: (1) Oak Ridge National Laboratory, gas chromatography/cryogenic enrichment (less than 10 ppbv sensitivity); (2) National Institute of Standards and Technology, gas chromatography/mass spectrometry/thermal conversion (less than 10 ppbv); (3) Ontario Hydro Technologies, Fourier transform infrared spectrometry (FTIR) (less than 100 ppbv). Studies showed that S{sub 2}F{sub 10} can be produced in the laboratory by corona, spark, and power arc discharges and that the production rates for each type of discharge decrease in that same respective order. In power arcs, SOF{sub 2} is by far the dominant species. The field survey provided baseline data and demonstrated the feasibility of taking and analyzing field samples using the techniques developed under this CRADA. It was found that in power arcs the amount of S{sub 2}F{sub 10} produced is relatively insignificant compared to the amount of the SOF{sub 2} produced. The knowledge gained from this CRADA should also be beneficial for the development of routine procedures for gas analysis, so that analysis of the decomposition products of SF{sub 6} will become a standard method for addressing the issues of health and safety, equipment reliability and aging, and diagnostics for GIS (Gas-Insulated Substations).

The Cooperative Research and Development Agreement (CRADA), established to study the production and mitigation of S/sub 2/F/sub 10/ (disulfur decafluoride), one of a number of toxic by-products formed in electric discharges in the insulating gas SF/sub 6/, is described. The particular concern about S/sub 2/F/sub 10/ is due to its highly toxic nature, the ceiling limit value being 10 parts per billion (ppb, or 1 part in 10/sup 8/), and the need for development of sensitive detection techniques down to this level. In the presence of an electrical discharge such as an arc, spark, or corona, a portion of the SF/sub 6/ decomposes into lower fluorides of sulphur which can react to form a number of chemically active by-products including SOF/sub 2/ and SO/sub 2/F/sub 2/. During the maintenance or repair of SF/sub 6/-insulated equipment, the handling of these gaseous is a matter of concern. Preliminary arc experiment results, reported health-related incidents caused by SF/sub 6/ by-products, and ongoing studies are discussed.< >

We identify a considerable improvement in proposed schemes for isotopic depletion of zirconium-91 on the basis of the atomic vapor laser isotope separation (AVLIS) method. The improvement lies in applying a single-longitudinal-mode dye laser for selective excitation of all hyperfine split levels of the ground state of zirconium-91. High-resolution laser-induced fluorescence spectroscopy of atomic beams of zirconium produced through laser vaporization–supersonic expansion has been used to identify transitions of zirconium with suitable hyperfine structure. Casimir magnetic-dipole and electric-quadrupole coupling constants and isotope shifts have been derived and are reported for five excited configurations. Suitable intermediate levels in a multistep resonance ionization pathway have been identified by two-color resonance ionization spectroscopy. Isotope depletion has been demonstrated on one ground-state-transition ( z F33∘←a F32at 593.7 nm) by using a specially constructed pulsed, single-longitudinal-mode dye-laser oscillator. Prospects and future directions in zirconium AVLIS are discussed.

Experimental measurements of small-signal gain in an optically-pumped NH3 amplifier are carried out at pressures ranging from 40 Torr to 760 Torr, and the results are used to validate a rate-equation model describing the amplifier dynamics. The gain measurements show that dilute mixtures of <0.5% NH3 in N2 are reqired to minimize the problems of gas heating due to pump absorption. The model is used to extrapolate the results to gas pressures of several atmospheres, and to demonstrate the potential for highpressure operation of optically-pumped NH3 lasers. For a pump intensity of 100 MW/cm2, calculations indicate that operation of an NH3−N2 laser is feasible up to a pressure of 10 atm, which would provide a maximum continuous tuning range of 4 cm−1. High-resolution spectroscopy reveals that gain on a few NH3 transitions is eliminated at high pressures due to the presence of overlapping absorptions in other NH3 bands.

The dynamics of pulsed line-tunable NH3 lasers are investigated by measuring small-signal gain as a function of NH3 transition, NH3 concentration, and pump intensity. Under typical experimental conditions, it is shown that the rotational populations in NH3 thermalize and that consequently the relative gain distribution can be described by a ratio of vibrational populations. Peak gains of 20% cm−1 are reported for mixtures of 4% NH3 in N2 pumped by the 9R(30) CO2 laser line. Heating that is due to increased pump absorption reduces the gain in mixtures of higher NH3 concentrations. The experimental results are in good agreement with the predictions of a rate-equation model, which can be applied to optimize line-tunable NH3 lasers.

To support its extensive program of heavy-water-moderated nuclear generation (which will reach a capacity of 14 GW by the early 1990s), Ontario Hydro has the world's largest production capacity for deuterium. This deuterium is produced in plants based on the bithermal exchange of hydrogen between hydrogen sulfide and water, which can produce in excess of 1000 tonnes/annum of pure D2O. Shortly, Ontario Hydro's involvement in hydrogen isotope production will be extended even further with the commissioning of a plant for separation of tritium from deuterium by means of cryogenic distillation of elemental hydrogen.

A cw CO2 laser operating on the R(30) 9-μm transition is downshifted by 180 MHz in a pair of acousto-optic modulators to give an exact coincidence with the sR (5, 0) transition in NH3. The downshifted radiation optically pumps mixtures of NH3 in N2 and creates vibrational inversion in the ν2 mode of NH3. This inversion is monitored with a tunable-diode laser operating in the 11–12-μm region. Gain coefficients as large as 3.4%/cm are measured in the P branch of the ν2 band, and the measured gain coefficients are found to be in good agreement with a rate-equation model based on rotational thermalization. Detailed measurements of gain coefficients are presented as a function of NH3 transition, pump power, and gas mixture and pressure. These results will aid in the optimization of cw NH3 lasers operating in the 11–13-μm region.

A novel two-step optical pumping technique is described for creating line-tunable laser emission in the 2ν2–ν2 band of NH3. Two TE CO2 lasers operating on the R(30) and P(24) 9-μm transitions are used to pump the sR(5,0) and 2sR(4,3) NH3 transitions respectively, and lasing is observed on 11 different NH3 lines having wavelengths from 16 to 21 μm. This pumping technique relies on rapid rotational thermalization in the vibrational levels to enhance the pump absorptions and distribute the population inversion. The possibility of producing cw line-tunable operation on these transitions is discussed.

In recent years the tunable diode laser (TDL) has emerged as a powerful tool for probing the gain dynamics of infrared gas lasers.1 For studies of laser dynamics, TDL’s are superior to more conventional oscillator-amplifier configurations because the wide tunability of the TDL allows both lasing and absorbing transitions to be probed. In addition, the high resolution and high sensi- tivity of the TDL technique allow measurement of spectral features that would be un- detectable by more conventional methods. We have recently reported on the first operation of a 12-μm cw NH3 laser, which was optically pumped at line center.2 To characterize this device we have made detailed small-signal-gain measurements of optically pumped NH3 and compared them with calculated values derived from a rate-equation model. In general, there is good agreement between the experiment and theoretical calculations.

Coherent effects produced by high-intensity pumping onaR(6, 0) in NH3are investigated for both the pure gas and for mixtures with an inert buffer gas. Two different Raman transitions are observed. One is the usual directly pumped Raman transition, and the other is pumped indirectly since it first requires a large population transfer to the upper vibrational level. This population transfer also creates inversion gain, shifted away from line center due to ac Stark shifts, on both transitions. Raman gain coefficients of 10 percent ċ cm-1and inversion gain coefficients > 2 percent ċ cm-1are observed, and compared to a combined density-matrix and rate-equation model.

The small-signal gain of a cw optically pumped 12-μm NH3 system is investigated as a function of pump intensity, pressure, pump offset, and polarization using a tunable diode laser as a probe. In general, the experiment is found to be in good agreement with calculations based on the theory of two laser fields interacting with a three-level molecular system. Raman gains in excess of 3%/cm are obtained using a waveguide configuration. The significance of these findings is discussed in terms of designing an efficient and powerful cw 12-μm laser.