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Pyongyang, South Korea

Ryo H.-S.,Kim Il Sung University | Ryo I.-G.,State Academy of science
Applied Physics A: Materials Science and Processing | Year: 2016

In this study, a generalized inverse-pole-figure (IPF) method has been suggested to analyze domain switching in polycrystalline ferroelectrics including composition of morphotropic phase boundary (MPB). Using the generalized IPF method, saturated domain orientation textures of single-phase polycrystalline ferroelectrics with tetragonal and rhombohedral symmetry have been analytically calculated and the results have been confirmed by comparison with the results from preceding studies. In addition, saturated domain orientation textures near MPBs of different multiple-phase polycrystalline ferroelectrics have been also analytically calculated. The results show that the generalized IPF method is an efficient method to analyze not only domain switching of single-phase polycrystalline ferroelectrics but also MPB of multiple-phase polycrystalline ferroelectrics. © 2016, Springer-Verlag Berlin Heidelberg.

Kim K.-H.,Max Born Institute For Nichtlineare Optik Und Kurzzeitspektroskopie | Kim K.-H.,State Academy of science | Griebner U.,Max Born Institute For Nichtlineare Optik Und Kurzzeitspektroskopie | Herrmann J.,Max Born Institute For Nichtlineare Optik Und Kurzzeitspektroskopie
Optics Express | Year: 2012

We theoretically study femtosecond pulse generation by passive mode-locking of semiconductor disk lasers operating in the blue spectral range using metal nanocomposites as slow saturable absorbers. By using the relation for the nonlinear dielectric response of a layer of silica glass doped with spherical silver nanoparticles and the master equation for modelocking we investigate the dynamics of pulse formation and the achievable pulse parameters and predict the generation of pulses as short as 50 fs at 420 nm in such lasers. ©2012 Optical Society of America.

Kim K.-H.,State Academy of science | Yurkin M.A.,Novosibirsk State University
Optics Express | Year: 2015

We develop the time-domain discrete dipole approximation (DDA), describing the temporal evolution of electric field in plasmonic nanostructures. The main equation is obtained by taking the inverse Fourier transform of the Taylor expansion of the frequency-domain DDA in terms of frequency deviation from the central frequency. Thus we assume that incident wavefronts of different frequencies accumulate relatively small phase difference when passing the particle. This assumption is always valid for nanoparticles much smaller than the wavelength. Being the time-domain method, the proposed approach also requires an analytic frequency dependence of electric permittivity, e.g. The Drude model. We present numerical results of application of the time-domain DDA to silver nanosphere, rod, and disk, which agree well with that obtained with its frequency-domain counterpart and the finite-difference time-domain method. Moreover, the time-domain DDA is the fastest of the three methods for incident pulses of several-femtoseconds width. Thus, it can effectively be applied for modeling the temporal responses of plasmonic nanostructures. © 2015 Optical Society of America.

We develop a theoretical model for the nondegenerate nonlinear optical susceptibility of dielectric composite materials containing metal nanoparticles. The model is based on the theory of transient nonlinear response of metal nanoparticles in combination with the effective medium approximation and the discrete dipole approximation. Its validity is confirmed by comparison with a preceding experimental result. Through numerical simulations, we demonstrate that for off-plasmon-resonant pumping the imaginary part of nondegenerate third-order nonlinear susceptibility becomes negative over a wide spectral range of signal. We additionally show the saturation effect of nondegenerate susceptibility depending on pump intensity and wavelength. © 2013 Astro Ltd.

Ri M.-H.,State Academy of science | Zhang P.,CAS Academy of Mathematics and Systems Science | Zhang Z.,Peking University
Journal of Mathematical Fluid Mechanics | Year: 2016

We prove global well-posedness for instationary Navier–Stokes equations with initial data in Besov space (Formula presented.) in whole and half space, and bounded domains of (Formula presented.) , (Formula presented.). To this end, we prove maximal (Formula presented.) -regularity of the sectorial operators in some Banach spaces and, in particular, maximal (Formula presented.) -regularity of the Stokes operator in little Nikolskii spaces (Formula presented.) , (Formula presented.) , which are of independent significance. Then, based on the maximal regularity results and (Formula presented.) estimates of the Stokes semigroups, we prove global well-posedness for Navier–Stokes equations under smallness condition on (Formula presented.) via a fixed point argument using Banach fixed point theorem. © 2016, Springer International Publishing.

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