I-Min Jiang

Surface plasmon enhanced diffraction in cholesteric liquid crystals

The authors report the observation of an enhanced optical diffraction in cholesteric liquid crystals (CLCs) due to the presence of silver nanoparticles. The silver nanoparticles are deposited on the surface of one of the indium tin oxide electrodes of the CLC cell. With the application of a proper voltage, the liquid crystals assume its cholesteric phase with the helical axis perpendicular to the applied electric field. The CLC grating was probed by a beam of polarized light in the spectral range from 450to750nm. The direction of propagation of the beam is perpendicular to the helical axis of the liquid crystals. The authors report a significant enhancement in the first-order diffraction efficiency at around 543nm. The results of the experimental observation are presented and discussed.

Dynamics of single-layer polymer breath figures

A single-layer of breath figure pattern was explored via the dynamical optical images and the temperature evolution. The pattern was prepared with the solution of carbon disulfide (CS(2)) dissolved 1% weight concentration of polystyrene. The evaporation of CS(2) was considered to be the most important role to the formation of the breath figure pattern. The understanding of the breath figures pattern will promote the technique to fabricating an imprinted template with demanded hexagonal structures.

Sensitive voltage-dependent diffraction of a liquid crystal Fresnel lens

This investigation proposes a Fresnel liquid crystal (LC) lens with high diffraction efficiency and a low driving voltage. A Fresnel zone electrode was fabricated on a glass plate. A Fresnel zone-distributed electric field in the LC cell was induced by a proper driving voltage, yielding a concentric structure of LCs as a Fresnel phase lens. A remarkable diffraction efficiency of ~39%, close to the theoretical limit of 40.5%, was detected when the LC lens was probed using a polarized incident beam with a wavelength of 632.8 nm. The diffraction efficiency of the Fresnel LC lens was demonstrated to depend sensitively on the applied voltage. The most suitable driving voltage of the Fresnel LC lens was as low as 0.9 V. This study may support progress in the electrical modulation of the optical properties of various optical systems.

SYNCHRONIZATION OF UNCERTAIN HYPERCHAOTIC AND CHAOTIC SYSTEMS BY ADAPTIVE CONTROL

This paper presents the synchronization between uncertain hyperchaotic and chaotic systems. Based on Lyapunov stability theory, an adaptive controller is derived to achieve synchronization of hyperchaotic and chaotic systems, including the case of unknown parameters in these two systems. The T.N.C. hyperchaotic oscillator is used as the master system, and the Rossler system is used as the slave system. Numerical simulations verify these results. Additionally, the effect of noise is investigated by measuring the mean squared error (MSE) of two systems.

Multiguide directional coupler using switchable liquid-crystalline optical channels

A multiguide directional coupler with a gratinglike indium-tin-oxide electrode on a planar nematic liquid-crystal film is studied. The linearly polarized beam can be coupled into adjacent channels with the periodic modulation of the refractive index by applying a periodic electric field. The intensity distribution of coupling in the transverse direction varies with the distance of beam propagation. The coupling effects, which depend on the polarization of the incident beam and the temperature of the liquid crystals, are also discussed.

Ordering formation of columnar lattices in magnetic fluid thin films subjected to oscillating perpendicular magnetic fields

Applying an oscillating magnetic field perpendicularly on the high-quality magnetic fluid thin film, the phase separation of particles in the liquid matrix will occur. The concentrated phase makes up the cylindrical columns that can form two-dimensional lattices. The ordered structure of magnetic fluid thin films is the basis for the potential optical application. We explore the dynamical ordering formation of columnar lattices in magnetic fluid thin films subjected to oscillating perpendicular magnetic fields in this study.

Atomic force microscopy study on the surface structure of oxidized porous silicon

Abstract We study the surface structure of porous silicon (PS) using atomic force microscopy (AFM), before and after oxidation in a HNO 3 solution. The AFM image shows the PS surface with a self-affine random fractal structure of wires, hillocks and voids in various scales. After oxidization the wires and hillocks of PS structures are glazed with oxide and the voids are filled. PS structure is altered to a simple self-affine fractal structure of hillock clusters. The fractal dimension D of PS is around 2.3, which decreases with increasing oxidization to about 2.0 of a smooth surface for the saturated oxidization. Our direct observation of the fractal structure of PS from AFM data reveals a good explanation for the recently found novel nonlinear dc-response in Ag thin films deposited on PS. We find the fractal surface structure of oxidized PS responds to the stepwise avalanche electric breakdown of the resistivity of Ag thin films deposited on oxidized PS.

The novel non-linear dc response of Ag thin films deposited on porous silicon: a fractal model explanation

We have observed a novel non-linear dc resistivity of Ag thin films deposited on porous silicon (PS) surfaces. We also found that as the porous silicon is oxidized in a HNO3 solution, the dc resistivities of the Ag thin films become two orders of magnitude smaller, and behave linearly but are divided into three different regions. Each region exhibits different resistivities which drops abruptly at the thresholds. The resistivity decreases as the current increasing into a higher current region. The atomic force microscopy (AFM) image shows a self-affine structure of the PS surface with wires, hillocks and voids on various scales. After oxidation, the rough surface is smoothed down to simpler fractal hillock clusters. The silver clusters are deposited on the glazed surface in a fractal-like size distribution. A branched Koch curve fractal model is proposed in this study to model the tunneling between fractal-like silver clusters. It explains the stepwise linear fractal-like resistivity behavior.

Surface plasmons induced extra diffraction band of cholesteric liquid crystal grating

Diffraction behavior of cholesteric liquid crystal (CLC) grating with the surface plasmon effect was investigated. One indium tin oxide plate of the CLC grating cell was covered with silver nanoparticles. With the application of a proper voltage, a well formed phase grating was constructed in the CLC cell. The CLC grating was probed by a beam of the polarized-monochromatic light, and the wavelength range was from 450 to 700 nm. It was shown that an extra first-order diffraction band was observed around 505 nm. The physical reason of the extra diffraction band could be the surface plasma effect emerged from silver nanoparticles. The extra diffraction band due to the surface plasmon effect can offer potential applications in nano-optics, such as the optical switch function.

Laser pulse induced gold nanoparticle gratings

We report the results of our experimental investigation of laser induced gold nanoparticle gratings and their optical diffraction properties. A single shot of a pair Nd-YAG laser pulses with the same polarization is directed toward a 6 nm thick gold film on a substrate of polymethyl methacrylate. As a result of the laser illumination, the thin gold film is fragmented into an array of nanoparticles. Through the observation of scanning electron and dark-field optical microscopes, we discovered that the morphology of the gold nanoparticle grating is dependent on the fluence of laser pulse. The spectrum of first order diffraction shows the dependence on the absorbance property due to the presence of the nanoparticles. The ablation of nanothickness thin films via the use of laser pulses may provide a simple and efficient method for the fabrication of nanoscale structures, including two dimensional arrays of nanoparticles.