Min Naiben

Preparation of Silver-Coated Polystyrene Composite Particles

We report a feasible approach to the preparation of monodispersed metal-shell composite microspheres based on a combination of surface reaction and surface seeding techniques. The method was implemented for coating polystyrene (PS) spheres with silver shell having a variable thickness by controlling the amount of reagents in the reaction procedure. These composite spherical particles in dimensions of the submicrometer range may become attractive building blocks for the creation of metallo-dielectric photonic band gap materials when they are organized into crystals.

Pure Electric and Pure Magnetic Resonances in Near-Infrared Metal Double-Triangle Metamaterial Arrays

We experimentally and numerically investigate the optical properties of metamaterial arrays composed of double partially-overlapped metallic nanotriangles fabricated by an angle-resolved nanosphere lithography. We demonstrate that each double-triangle can be viewed as an artificial magnetic element analogous to the conventional metal split-ring-resonator. It is shown that under normal-incidence conditions, individual double-triangle can exhibit a strong local magnetic resonance, but the collective response of the metamaterial arrays is purely electric because magnetic resonances of the two double-triangles in a unit cell having opposite openings are out of phase. For oblique incidences the metamaterial arrays are shown to support a pure magnetic response at the same frequency band. Therefore, switchable electric and magnetic resonances are achieved in double-triangle arrays. Moreover, both the electric and magnetic resonances are shown to allow for a tunability over a large spectral range down to near-infrared.

Optical Anisotropic Properties of m-Plane GaN Film Grown by Metalorganic Chemical Vapor Deposition

Abstract Spontaneous and piezoelectric polarization could lower the efficiency of GaN-based light-emitting diodes. In order to eliminate or reduce this undesirable effect, m-plane GaN film was prepared by metalorganic chemical vapor deposition (MOCVD) on LiAlO 2 (100) substrate with a GaN buffer layer. Since the c axis of the m-plane GaN lays in the grown plane, the breakage of in-plane symmetry gave rise to an optical anisotropy, which was revealed by a difference in refractive indexes of E-field parallel and perpendicular to the c axis of the m-plane GaN measured by polarized reflection measurement. In addition, in-plane strain anisotropy due to the lattice mismatch between the GaN film and the LiAlO 2 substrate changed the Electronic Band Structure (EBS). The change of EBS also led to an in-plane optical anisotropy. Polarized absorption and Photoluminescence (PL) measurements showed a split in energy of 32 meV for optical absorption edge and 37 meV for PL peak energy respectively.

Red and Blue Light Generation in an LiTaO3 Crystal with a Double Grating Domain Structure

The Pd39Ni10Cu30P21 bulk metallic glass is isothermally relaxed under various pressures. The degree of the structural relaxation is evaluated in terms of the enthalpy recovery behaviours involved in the irreversible glass transition processes by using a temperature-modulated differential scanning calorimetry technique. A roughly Linear increase of the recovery enthalpy is observed within the experimental pressure range fi-om 2.67 to 4.45 GPa, which reflects the release of the frozen-in enthalpy in the as-quenched glass with increasing relaxation pressure. The pressure dependence of the timescale of the enthalpy recovery processes is also exhibited.

Thermal Expansion of CsNiCl3 by Electron Paramagnetic Resonance and Optical Absorption Spectra

Electron paramagnetic resonance (EPR) measurement of CsNiCl3 compound has been performed at 192 GHz in the temperature range from 300 to 5 K, along the axes of main g tensor. The energy levels and the g-factors are calculated. The linear thermal expansion coefficient (2.77×10-5 K-1) for the Ni2+-Cl- bond distance is studied by combining EPR and optical absorption spectra with changing temperature.

A Study of 90° Ferroelectric Domain Structures in PbTiO3 Thin Films by Means of Transmission Electron Microscopy

PbTiO3 thin films prepared by metalorganic chemical vapor deposition method were investigated using a transmission electron microscope. The as-deposited thin films were highly c-axis oriented, 90° a-c domains were observed and their crystallographic characteristics were investigated. Tetragonality of the PbTiO3 films was also obtained. The disappearance of 90° domains in the very thin film was found and attributed to surface relaxation effect.

Efficient Generation of Red and Blue Light in a Dual-Structure Periodically Poled LiTaO3 Crystal

We demonstrate the efficient generation of red light at 671 nm and blue light at 447 nm from a diode-pumped Q-switched 1342 nm Nd:YVO4 laser together with a periodically poled LiTaO3 (PPLT) crystal. The sample used in this experiment is a dual-structure PPLT crystal with the period of 14.9 μm for the second harmonic generation and that of 4.9 μm for the third harmonic generation. The red and blue light, with the respective average power of 752 mW and 153 mW were obtained in a single path under an average fundamental power of 1.74 W, corresponding to the conversion efficiencies of 43.2% and 8.8%, respectively. These results indicate that the dual-structure PPLT can be used to construct a compact and efficient all-solid-state red-and-blue dual-wavelength laser.

Engineered ferroelectric superlattice materials and applications

The study of superlattice based on ferroelectric crystal has made a rapid progress since 1980s. The superlattice is composed of modulated domains on the micron scale controllable with modern techniques. A lot of new phenomena have been techniques for fabrication and characterization, and in exploring new physical effects for the nonlinear-optical applications.

A New Type of Bistable Switching in Two-Dimensional Nonlinear Optical Superlattices

We investigate theoretically optical response in a two-dimensional optical superlattice with Kerr-type nonlinearity. We find that in addition to the bistability reported in Phys. Rev. Lett. 71 (1993) 1003 by Xu et al., a new type of bistable switching behavior exists. This bistability is based on the occurrence of the stop gap in the linear spectra and the nonlinear mechanism on it, which makes switching between transmitting and non-transmitting states achievable.

Optical Bistability in Incident-Dependent Two-Dimensional Nonlinear Optical Superlattices

It is shown that, when two coherent waves are obliquely incident to a one-dimensional nonlinear optical superlattice containing Kerr-form dielectric nonlinearity, an incident-dependent two-dimensional nonlinear optical superlattice can be constructed. This structure can be bistable. There exist two types of optical bistable mechanism, i.e., the index-modulation mechanism and distributed feedback mechanism. Owing to the index-modulation mechanism, the threshold for the bistability is lower than that of a more traditional one-dimensional distributed feedback structure.