A power-scaling strategy for longitudinally diode-pumped Tm:YLF lasers

We describe a power-scaling strategy for longitudinally diode-pumped Tm:YLF lasers based on optimisation of the thulium doping level and the gain geometry. Carefully designed laser experiments at lower powers are shown to allow a simple means for accurately predicting the thermal loading and hence the power-scaling properties of this system, including the effects of ground-state depletion, cross relaxation and energy-transfer upconversion. An optimised doping level of 2 at. % and a slab geometry are shown experimentally to allow scaling of a single gain unit to output powers of ∼70 W, limited by the available pump power, and a strategy for scaling well beyond 100-W output is discussed. PACS 42.55.-f; 42.55.Xi; 42.60.By     

Semileptonic decays of d mesons in three-flavor lattice QCD

We present the first three-flavor lattice QCD calculations for D-->pilnu and D-->Klnu semileptonic decays. Simulations are carried out using ensembles of unquenched gauge fields generated by the MILC Collaboration. With an improved staggered action for light quarks, we are able to simulate at light quark masses down to 1/8 of the strange mass. Consequently, the systematic error from the chiral extrapolation is much smaller than in previous calculations with Wilson-type light quarks. Our results for the form factors at q(2)=0 are f(D-->pi)(+)(0)=0.64(3)(6) and f(D-->K)(+)(0)=0.73(3)(7), where the first error is statistical and the second is systematic, added in quadrature. Combining our results with experimental branching ratios, we obtain the Cabibbo-Kobayashi-Maskawa matrix elements |V(cd)|=0.239(10)(24)(20) and |V(cs)|=0.969(39)(94)(24), where the last errors are from experimental uncertainties.     

Detailed topography of the fermi surface of Sr2RuO4

We apply a novel analysis of the field and angle dependence of the quantum-oscillatory amplitudes in the unconventional superconductor Sr2RuO4 to map its Fermi surface (FS) in unprecedented detail and to obtain previously inaccessible information on the band dispersion. The three quasi-2D FS sheets not only exhibit very diverse magnitudes of warping, but also entirely different dominant warping symmetries. We use the data to reassess recent results on c-axis transport phenomena.     

Ion-exchanged tapered-waveguide laser in neodymium-doped BK7 glass

We report what is to our knowledge the first operation of a planar dielectric tapered-waveguide laser. The waveguide laser is fabricated by potassium-ion exchange in Nd(3+) -doped BK7 glass and consists of a single-mode channel waveguide of a few micrometers' width followed by a linear taper up to a broad region with a width of ~180microm . A slope efficiency of 42% is found both in the tapers and in standard channel waveguides fabricated upon the same substrate, indicating that the tapers and the channels have similar internal losses; hence the low-loss nature of the tapered beam expansion. The output from either end of the tapered structure is found to be nearly diffraction limited.     

Infrared absorption and structure of chlorophosphate glasses

The infrared absorption spectra of glasses in the NaPO₃---ZnCl₂ system were studied in the range of 4000−350 cm⁻¹. The results were interpreted using a local mode approach based on existing frequency charts. A continuous structural breakdown of the glass structure occurs upon addition of ZnCl₂ to the NaPO₃ polymer, with a consequent decrease in its chain length. The actual structure of the chlorophosphate glasses is discussed on the basis of possible anionic groups present. There is evidence for the occurrence of mixed oxychloride coordination shells. The density and glass transition temperature of the glasses were also determined.     

Raman and mid-infrared spectroscopic study of the phase transitions in octafluoronaphthalene at elevated pressures

Raman and mid-infrared spectra of C₁₀F₈ have been obtained under hydrostatic pressures up to 17 kbar in a diamond anvil cell. The C₁₀F₈ I–II phase change, previously observed by neutron diffraction at about 0.8 kbar, has been confirmed. No evidence was found to support the existence of a furtt ier phase change between 4 and 6 kbar indicated by the neutron work, although this is certainly not precluded as the extra spectral features expected in this case are extremely small. The mode Grüneisen parameters, γ_i, allow a clear distinction between internal and external molecular modes, and scale roughly in accord with Zallen's relation γ_i$\text{\$}\text{?}$v_i^?2.     

Observation of surface characteristics by DSC and DTA

The three types of hydroxyl groups on surfaces of goethite crystals have previously been shown to be distinguishable by inflections on the leading edge of the dehydroxylation endotherm on DSC curves. The same inflections can be observed on DTA curves and it is now established that the main prerequisite for their observation is rapid removal of water vapour from particle surfaces, although small particle size (i.e. large surface area) and uncontaminated surfaces are also important.

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Zusammenfassung Bei den drei Typen von Hydroxylgruppen an den Oberfläche von Goethitkristallen wurde zuvor festgestellt, daß sie durch den Wendepunkt an der Leitkante der Dehydroxylierungs-Endothermen an den DSC-Kurven zu unterscheiden sind. Dieselben Wendepunkte können auch an DTA-Kurven beobachtet werden und es steht nun fest, daß die Hauptvoraussetzung ihrer Beobachtung in der schnellen Entfernung des Wasserdampfes von der Teilchenoberfläche besteht, obwohl die kleine Teilchengrösse (d. h. eine grosse spezifische Oberfläche) und unkontaminierte Oberflächen auch von Bedeutung sind.

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The authors wish to express their sincere thanks to Mr E. L. Charsley of Stanton Redcroft Consulting Service for very kindly carrying out a determination on the STA-780 apparatus.     

The study of catalysis by novel gas chromatographic techniques

Summary Studies of catalytic reactions have been made using differential (sample-vacancy) and stopped-flow gas chromatography. Reactions are often very sensitive to trace materials and in particular it has been necessary to devise a technique for removing oxygen from carrier-gas streams down to very low levels. The techniques and the results are often relevant to the more normal analytical applications of gas chromatography.Presented at Table Ronde sur les mesures physicochimiques par chromatographie en phase gazeuse (Lyons, November 13–14th, 1973), organized by Dr.robin (INSA, Villeurbanne)