A new approach (ThinZag®) for scaling Nd:YAG solid-state slab lasers to high power levels is described. Using an innovative optical configuration, thin slabs of solid-state gain material are immersed in a flowing cooling fluid, resulting in improved thermal management. Measurements at the ~1 kW level were conducted to compare Nd:YAG ceramic with Nd:YAG crystalline slabs. The ceramic slabs demonstrated comparable laser output power relative to the more standard crystalline slabs and demonstrated better optical properties, which result in improved medium uniformity. Performance results from our nominally 5 kW and 15 kW modules are also presented. The 15 kW modules represent basic building blocks for the Joint High Power Solid State 100 kW Laser (J-HPSSL) currently being designed and developed by Textron Defense Systems. Recent measurements of three nominally 15 kW modules operating as a single aperture power oscillator where outputs to 30 kW with beam quality of 3.3 XDL were measured are also included. The reported powers were for operation below maximum pump rate of the device.

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A crossed molecular beam study has been made of reactive cross section as a function of collision energy Sr(ET) for all isotopic variants of the abstraction reaction H′+H″Br→H′H″+Br. The apparatus incorporates, for reagent preparation, a supersonic source of variable-energy H or D atoms, and, for product detection, a tunable vacuum ultraviolet laser to obtain laser-induced fluorescence of Br. The cross-section functions indicate that the threshold energy for reaction is <1 kcal/mol. At enhanced collision energy of ET = 7 kcal/mol, the observed order of reactivity in the isotopic series designated (H′,H′′) was (D,H)≳(D,D)≳(H,H)≳(H,D). As noted in a previous report from this laboratory [Int. J. Chem. Kinet., Laidler Festschrift (in press)] the favorable kinematics for (D,H) as compared with (H,D) can be understood in terms of lengthened interaction time for D atom reaction (compared with H) and diminution in the time required for HBr (compared with DBr) to rotate into the preferred alignment for reaction. The effect is illustrated here in terms of a simple model of reaction. The experimental data obtained in this work at low collision energy, in conjunction with 300 K rate constants obtained by others, suggest that close to threshold, kinematic effects are supplanted by threshold effects, yielding Sr(H,D)≳Sr(D,H), the inverse of the principal isotope effect at enhanced collision energy.

Comparison of variational transition state theory and quantum sudden calculations of threedimensional rate coefficients for the reactions D(H)+BrH→DBr(HBr)+H

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