Highly efficient, 0.84 slope efficiency, 901 nm, quasi-two-level laser emission of Nd in strontium lanthanum aluminate

The possibility of using direct pumping into the emitting level of the Nd3+ ion in magnesium-compensated strontium lanthanum aluminate (Sr(1-x)La(x-y)Nd(y)Mg(x)Al(12-x)O19) to improve 900 nm 4F(3/2) --> 4I(9/2) laser emission is discussed. Selection of the composition parameters x and y for optimization of laser emission and reduction of heat generation is based on the spectroscopic and crystal growth characteristics. Pumping in the 865.5 nm absorption band 4I(9/2)(Z1) --> 4F(3/2)(R1) transforms the laser process into a quasi-two-level scheme of very low (below 4%) quantum defects. A very high slope efficiency (over 84%) for 901 nm continuous-wave laser emission is demonstrated with Ti:sapphire laser pumping in this band for a crystal with x = 0.4 and y = 0.05.     

Apatite-structure crystal, Yb(3+):SrY(4)(SiO(4))(3)O, for the development of diode-pumped femtosecond lasers

We report what is believed to be the first diode-pumped Yb(3+): SrY(4)(SiO(4)) (3)O laser. We investigate both the cw and the mode-locked regimes. In the cw regime an average output power of 1.05 W is demonstrated for 3.6 W of incident pump power. In the femtosecond regime a pulse duration of 94 fs for an average power of 110 mW is obtained at a central wavelength of 1068 nm. This is, to our knowledge, the first femtosecond mode-locked oscillator made with an Yb-doped apatitelike crystal. These properties are related to the unique spectroscopic properties of Yb(3+) ions in this atypical apatite-family crystal.     

Dynamics of flow–soot interaction in wrinkled non-premixed ethylene–air flames

A two-dimensional simulation of a non-premixed ethylene–air flame was conducted by employing a detailed gas-phase reaction mechanism considering polycyclic aromatic hydrocarbons, an aerosol-dynamics-based soot model using a method of moments with interpolative closure, and a grey gas and soot radiation model using the discrete transfer method. Interaction of the sooting flame with a prescribed decaying random velocity field was investigated, with a primary interest in the effects of velocity fluctuations on the flame structure and the associated soot formation process for a fuel-strip configuration and a composition with mature soot growth. The temporally evolving simulation revealed a multi-layered soot formation process within the flame, at a level of detail not properly described by previous studies based on simplified soot models utilizing acetylene or naphthalene precursors for initial soot inception. The overall effect of the flame topology on the soot formation was found to be consistent with previous experimental studies, while a unique behaviour of localised strong oxidation was also noted. The imposed velocity fluctuations led to an increase of the scalar dissipation rate in the sooting zone, causing a net suppression in the soot production rate. Considering the complex structure of the soot formation layer, the effects of the imposed fluctuations vary depending on the individual soot reactions. For the conditions under study, the soot oxidation reaction was identified as the most sensitive to the fluctuations and was mainly responsible for the local suppression of the net soot production.     

Yrast and side bands in the odd-odd160, 162Tm nuclei

High-spin states in²⁰⁵Bi, populated in the²⁰⁵Tl(α, 4n) reaction with bombarding energies around 50 MeV have been studied usingγ-ray spectroscopic techniques. Spins and parities have been assigned on the basis of angular distribution andγ-ray linear polarization measurements. States with spins up to 39/2⁺ and excitation energies around 6 MeV have been identified. Calculations using the empirical shell model have been performed in order to assign configurations.     

L ∞ stability of the MUSCL methods

We present a general L ^∞ stability result for generic finite volume methods coupled with a large class of reconstruction for hyperbolic scalar equations. We show that the stability is obtained if the reconstruction respects two fundamental properties: the convexity property and the sign inversion property. We also introduce a new MUSCL technique named the multislope MUSCL technique based on the approximations of the directional derivatives in contrast to the classical piecewise reconstruction, the so-called monoslope MUSCL technique, based on the gradient reconstruction. We show that under specific constraints we shall detail, the two MUSCL reconstructions satisfy the convexity and sign inversion properties and we prove the L ^∞ stability.     

Issue Information

This paper describes a numerical discretization of the compressible Euler equations with a gravitational potential. A pertinent feature of the solutions to these inhomogeneous equations is the special case of stationary solutions with zero velocity, described by a nonlinear partial differential equation, whose solutions are called hydrostatic equilibria. We present a well‐balanced method, meaning that besides discretizing the complete equations, the method is also able to maintain all hydrostatic equilibria. The method is a finite volume method, whose Riemann solver is approximated by a so‐called relaxation Riemann solution that takes all hydrostatic equilibria into account. Relaxation ensures robustness, accuracy, and stability of our method, because it satisfies discrete entropy inequalities. We will present numerical examples, illustrating that our method works as promised. Copyright © 2015 John Wiley & Sons, Ltd.     

Multiwatt, tunable, diode-pumped CW Yb:GdCOB laser

We demonstrate that Yb-doped Ca₄GdO(BO₃)₃ (GdCOB) crystals are suitable for the development of high-power diode-pumped lasers emitting at around 1.04 μm. A 15%-doped Yb:GdCOB crystal was longitudinally pumped with a cw fiber-coupled diode emitting 10 W at 976 nm. While 5.2 W of diode power was absorbed, we obtained 3.2 W of 1043-μm laser light, with a beam quality factor M² equal to 3, and 2.5 W in a diffraction-limited beam. Furthermore, the laser is continuously tunable between 1018 and 1086 nm. Thermal effects have been investigated with a Shack–Hartmann wavefront analyser: although thermal lensing is not negligible, it does not affect the performance of the laser with the resonator design we used. Received: 1 August 2000 / Revised version: 18 September 2000 / Published online: 21 February 2001