Investigation into the power-law dependence of fibre Bragg grating growth

We have undertaken a detailed experimental and numerical investigation of fibre Bragg grating growth rates over relatively long timescales, in which we consider the influence of zero-order UV irradiation, jitter and drift. In contrast to other studies, our results show that measurements of grating growth dynamics are in good agreement with numerical expressions describing exponential decay of a population of defect sites if the influence of small lateral displacements between the optical fibre and the modulated UV beam (jitter) are accounted for.     

Slope efficiency of up to 73% for Yb:Ca4YO(BO3)3 crystal laser pumped by a laser diode

Yb:Ca₄YO(BO₃)₃ (Yb:YCOB) crystal with good quality and large size has been grown by the Czochralski method. The polarization absorption and fluorescence spectra have been measured. The laser action of the Yb:YCOB crystal has been demonstrated when it is pumped by a fiber-coupled laser diode (LD) at the wavelength of 976.4 nm. The pumping threshold is 55 mW, the light-light conversion efficiency is 58.7%, and a slope efficiency of up to 73% is thus calculated. Received: 16 December 1998 / Revised version: 4 February 1999 / Published online: 7 April 1999     

Using simultaneous diagonalization and trace minimization to make an efficient and simple multidimensional basis for solving the vibrational Schrodinger equation

In this paper we improve the product simultaneous diagonalization (SD) basis method we previously proposed [J. Chem. Phys. 122, 134101 (2005)] and applied to solve the Schrodinger equation for the motion of nuclei on a potential surface. The improved method is tested using coupled complicated Hamiltonians with as many as 16 coordinates for which we can easily find numerically exact solutions. In a basis of sorted products of one-dimensional (1D) SD functions the Hamiltonian matrix is nearly diagonal. The localization of the 1D SD functions for coordinate qc depends on a parameter we denote alphac. In this paper we present a trace minimization scheme for choosing alphac to nearly block diagonalize the Hamiltonian matrix. Near-block diagonality makes it possible to truncate the matrix without degrading the accuracy of the lowest energy levels. We show that in the sorted product SD basis perturbation theory works extremely well. The trace minimization scheme is general and easy to implement.     

Unstructured pressure‐correction solver based on a consistent discretization of the Poisson equation

A finite volume incompressible flow solver is presented for three‐dimensional unsteady flows based on an unstructured tetrahedral mesh, with collocation of the flow variables at the cell vertices. The solver is based on the pressure‐correction method, with an explicit prediction step of the momentum equations followed by a Poisson equation for the correction step to enforce continuity. A consistent discretization of the Poisson equation was found to be essential in obtaining a solution. The correction step was solved with the biconjugate gradient stabilized (Bi‐CGSTAB) algorithm coupled with incomplete lower–upper (ILU) preconditioning. Artificial dissipation is used to prevent the formation of instabilities. Flow solutions are presented for a stalling airfoil, vortex shedding past a bridge deck and flow in model alveoli. Copyright © 2000 John Wiley & Sons, Ltd.