Second harmonic generation from corona-poled polymer thin films of Y-shape chromophore with different isolation groups

We characterize thermal stability fof second harmonic generation (SHG) properties of four different Y-type polymers poled using corona poling method. These polymers are based on donor–acceptor–donor-type repeating unit with different aromatic moieties acting as donors and dicyanomethylene acting as an acceptor through conjugated bridge. The donor varies from different substituted benzene to phenothiazine. Polymer containing phenothiazine as donor showed higher SHG intensity and high temperature stability due to rigid repeating unit of phenothiazine compared to others with benzene in the main chain.     

OPTICAL ABSORPTION AND EMISSION STUDIES ON LASER DYE INCORPORATED IN NAFION MEMBRANE

Abstract— Incorporation of the laser dye 7-amino-4-methyl coumarin (C-120) in a perfluoro sulfonate cation exchange membrane (Nafion) from aqueous solution has been studied by following its light absorption and emission (fluorescence) characteristics. It is shown that in the H⁺ form of the membrane the dye exists in its monoprotonated cationic form, whereas in different cation exchanged forms of the membrane it is incorporated as the unprotonated neutral molecules. By repeated equilibration with the aqueous solution, high concentrations of the dye could be loaded into the membrane. As compared to an aqueous solution, the polymer matrix was found to confer very good photostability to the dye.     

Linearity stabilizes discrete breathers

The study of the dynamics of 1D chains with both harmonic and nonlinear interactions, as in the Fermi–Pasta–Ulam (FPU) and related problems, has played a central role in efforts to identify the broad consequences of nonlinearity in these systems. Here we study the dynamics of highly localized excitations, or discrete breathers, which are known to be initiated by the quasistatic stretching of bonds between adjacent particles. We show via dynamical simulations that acoustic waves introduced by the harmonic term stabilize the discrete breather by suppressing the breather’s tendency to delocalize and disperse. We conclude that the harmonic term, and hence acoustic waves, are essential for the existence of localized breathers in these systems.     

Switching behaviour of nonlinear Mach–Zehnder interferometer based on photonic crystal geometry

Nonlinear Mach–Zehnder interferometer (NMZI) created with photonic crystal waveguides (PCW) and with Kerr-type nonlinearity has been investigated in this paper. The NMZI has been simulated using two-dimensional finite difference time domain (2D-FDTD) method. Input verses output (I /O) characteristics have been obtained for different lengths of the nonlinear arm, nonlinear coefficients of the nonlinear arm, wavelengths of the input beam, sizes of defect rods and NMZI offset. The results obtained are compared with earlier published results of NMZI created with conventional step index waveguides (SIW). It is shown that all useful features of light switching offered by SIW-based NMZIs are also possible with PCW-based NMZIs of extremely small dimensions. Moreover, PCW-based NMZIs offer additional useful feature not available with SIW-based NMZIs.     

A Cutting-Point Technique For Solving Nonlinear State Regulator Problems

In this paper, we present a technique for solving an optimizationproblem of Lagrange type where the system equations are stiffand the system can be expressed explicitly in terms of a singular-perturbationparameter. Such problems arise in control theory and in otherapplication areas. The proposed procedure consists of solvingthe singularly perturbed two-point boundary-value problem comprisedby the coupled state and adjoint equations arising from thefirst-order necessary conditions for optimality. It is assumedthat the coupled system has no turning points, and the solutionis accomplished by making an analytic stretching in the boundarylayers to give three explicit boundary-value problems whichare treated separately. The novel feature of the procedure isthat the explicit boundary conditions for each problem are obtained,at the selected cut points, from the solution to the reducedproblem. The application of the procedure is described for twoexamples.