Integral cross sections for electron scattering by ground state Ba atoms

We have used the convergent close-coupling method and a unitarized first-order many-body theory to calculate integral cross sections for elastic scattering and momentum transfer, for excitation of the 5d^2 ^1S, 6s6p^1P_1, 6s7p^1P_1, 6s8p^1P_1, 6s5d^1D_2, 5d^2^1D_2, 6s6d^1D_2, 6p5d^1F_3, 6s4f^1F_3, 6p5d^1D_2, 6s6p^3P_{0,1,2}, 6s5d^3D_{1,2,3}, and 6p5d^3D_2 states, for ionization and for total scattering by electron impact on the ground state of barium at incident electron energies from 1 to 1000 eV. These results and all available experimental data have been combined to produce a recommended set of integral cross sections.Comment: 47 pages, 8 tables, 25 figure

Solid-state laser system for laser cooling of Sodium

We demonstrate a frequency-stabilized, all-solid laser source at 589 nm with up to 800 mW output power. The laser relies on sum-frequency generation from two laser sources at 1064 nm and 1319 nm through a PPKTP crystal in a doubly-resonant cavity. We obtain conversion efficiency as high as 2 W/W^2 after optimization of the cavity parameters. The output wavelength is tunable over 60 GHz, which is sufficient to lock on the Sodium D2 line. The robustness, beam quality, spectral narrowness and tunability of our source make it an alternative to dye lasers for atomic physics experiments with Sodium atoms

All-solid-state parametric Raman anti-Stokes laser at 508 nm

We report a parametric anti-Stokes Raman laser using potassium gadolinium tungstate, generating output chiefly at the first anti-Stokes at 508 nm. The compact 4.5 cm long device is pumped by a Q-switched 532 nm laser and uses an off-axis Stokes resonator to provide non-collinear phase matching between the pump and the generated Stokes and anti-Stokes fields. Anti-Stokes output energies up 0.27 mJ were obtained at a conversion efficiency from the pump of 0.46%. Second- and third-order anti-Stokes lines at 486 nm and 465 nm were also observed.9 page(s

Geomechanical fault characterization: impact on quantitative fault seal risking

Copyright © 2002 Society of Petroleum Engineers Inc. Published Paper ; 78213 Abstract Fault sealing is one of the key factors controlling hydrocarbon accumulations and can be a significant influence on reservoir behavior during production. Fault seal is, therefore, a major exploration and production uncertainty that requires a rigid, systematic framework within which to quantify the geological risk of trapping hydrocarbons. One of the key uncertainties in this risking procedure is the breaching of structurally bound traps due to the formation of structural permeability networks. Considering a population of faults and fractures, those that are critically stressed are more prone to act as conduits for fluid transmission. Evaluation and mapping of fault seal breach through such networks involves integration of in-situ stress conditions, pore pressure, fault architecture and fault geomechanics. Geomechanical characterization of well-lithified fault rocks from the Otway Basin and the Northwest Shelf demonstrates that faults can exhibit significant cohesive strength and that fault reactivation and trap breach is influenced by the development of shear, tensile and mixed-mode fractures. The mechanics of the reactivation process are influenced by grain strength and fault morphology. Mercury injection capillary pressures of cataclastic faults indicate a seal capacity of 2400 psi. Following reactivation, seal capacity is reduced ~95% due to the development of a highly connected fracture network. The tensile strength of such healed faults allows failure to occur by shear, tensile and mixed mode fracturing. These data suggest simple application of Byerlee's Law may not always be applicable when predicting reactivation induced fault seal failure. Consequently, geomechanical tools used to predict trap breach via reactivation that assume cohesionless frictional failure are likely to significantly underestimate seal reactivation risk. The impact of structurally risking traps using Byerlee and laboratory-derived fault data is demonstrated using the Fault Seal Risk Web approach. Application of geomechanical fault data results in a significant reappraisal of prospect structural risk due to consideration of fault healing. Introduction Hydrocarbon exploration and production strategies all involve an element of risk. As with any investment strategy it is the goal of the venture capitalist to minimize this risk. Geological risk minimization begins within a focused evaluation as to the chance of success, i.e. determining the likelihood that all elements of the petroleum system required for economically viable volumes of hydrocarbons to be trapped and developed have been satisfied. The presence of a sealed trap is one of the key factors in the evaluation of geological risk1,2,3. A seal is a barrier to the migration of hydrocarbons, either vertically to shallower strata or laterally across faults. According to the mechanism of failure, seals can be considered membrane or hydraulic4. Figure 1 illustrates the classification of seal by geometric type and process. Faults seal if they juxtapose reservoir rocks against sealing rocks5,6,7. Fault planes themselves seal if the faulting process has generated a membrane seal, for example by cataclasis8, cementation/diagenesis9, framework grain-clay mixing9 or clay smearing10. However, juxtaposition or deformation process seals may be breached if the fault is reactivated subsequent to hydrocarbons charging the trap. It is not necessary for both juxtaposition and deformation process seals to be developed in order for a fault to be sealing. If throw on the fault juxtaposes sealing rocks against reservoir rocks, no deformation process seal is required. Conversely, faults can seal where there is sand/sand juxtaposition across the fault plane and cataclastic processes have reduced pore throat sizes such that the fault zone itself acts as a membrane seal. Richard M. Jones, David N. Dewhurst, Richard R. Hillis, S.D. Mildre

Microstructural and geomechanical characterisation of fault rocks from the Carnarvon and Otway Basins

The results of natural and laboratory-induced fault behaviour from wells in the Otway Basin are compared with sample material from a producing Carnarvon Basin field where rocks from a fault zone have been cored. Capillary pressure, microstructural and juxtaposition data obtained from these fault rocks indicate a capability to hold back gas columns in excess of 100 m, yet many fault closures are found to contain only palaeo-columns. Trap failure is usually attributed to reactivation of trap-bounding faults, often during Miocene-Recent times in these basins. Faults susceptible to reactivation can be predicted by geomechanical methods involving the determination of the in-situ stress field and the orientation and dip of faults with respect to that stress field. Failure envelopes of fault rocks have been determined to estimate reactivation potential in the present day in-situ stress field. This approach works well where fault rocks are weaker than the host reservoir sandstone, but may not be applicable where fault rocks are stronger. In fields where the latter is the case, intact hydrocarbon columns are present, irrespective of whether faults are optimally oriented for reactivation. This indicates that the assumptions of zero cohesive strength and constant friction coefficient for predicting the reactivation potential of fault rocks may not be completely reliable

Optical microscopy imaging and image-analysis issues in laser cleaning

In earlier work we characterised single-pulse laser cleaning of medium-density (areal coverage 10–20%) alumina particles from glass surfaces with three different lasers. The method of measuring particle-removal efficiency involves optical microscopy imaging (digital) and subsequent image analysis of the area covered by, and/or the number of, particles before and after the single-pulse laser cleaning treatment. The sample-preparation technique used leads to both single particles and agglomerates on the surface. The issues of depth of focus in the imaging and grey-scale thresholding in the image analysis of such samples, with a range of particle and agglomerate sizes, has been systematically investigated. A protocol for optimum imaging and illumination of such samples is described herein. It has been developed based on the results of a systematic investigation of the effect of the image focal plane position relative to the surface also described herein. The image analysis to quantify the particles on the surface involves a judgement of the best threshold grey-scale level in the image to define the boundary between particles and background substrate. A quantitative appraisal of the impact on the laser cleaning efficiency results of a threshold grey-scale level that is set too high or too low, and how these results compare with those obtained for the "best-judgement" threshold grey-scale level, has been completed.7 page(s

Plasma relaxation processes in a small-scale kinetically enhanced copper vapour laser operating at elevated pulse repetition rates (50-70kHz)

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Diamond raman lasers

We summarize our recent research in Raman lasers based on undoped single crystal diamond. Highly efficient visible external cavity lasers operating in nanosecond and picosecond regimes are reported.2 page(s

Anomalous discharge mode in a kinetically-enhanced copper vapor laser : visualization by "hook" method

An anomalous discharge mode of a kinetically-enhanced copper vapor laser is reported. Under conditions of high-HCl density, the discharge makes an abrupt transition into a mode which is identified by a near field laser beam profile having a green (511 nm) central spot on a yellow (578 nm) background. Hook-method measurements reveal that a steep channel is produced in the radial Cu density profile, which forms a strong plasma lens duct for wavelengths nearby Cu resonance.2 page(s