Kinetic and Size Control of Polystyrene and Polyacrylic Octadecyl Ester Lattices Via Polymerization in O/W Microemulsions

The kinetic studies of the acrylic octadecyl ester and styrene polymerization in microemulsion systems, (1) cetyl pyridine bromide (CPDB)/t-butanol/styrene/water; (2) CPDB/t-butanol/toluene + acrylic octadecyl ester (1:1, w/v)/ water; (3) cetyl pyridine bromide/styrene/formamide, were made by using dynamic laser light scattering techniques (DLS). The mechanisms of nucleation of latex particles were discussed. The most possible nucleation location of the styrene and acrylic octadecyl ester microlatex particles in aqueous microemulsion system is in aqueous phase via homogeneous nucleation. Meanwhile, parts of microlatex particles are possibly produced via swollen micelles (microemulsions) and monomer droplets nucleation. On the other hand, the most possible nucleation location of the styrene microlatex particles in nonaqueous microemulsion system is inside monomer droplets. The relationship between the amount of monomer and the size of microlatex was also investigated. It has been found that the size of microlatex particles could be controlled by changing the amount of monomer. (C) 2002 Elsevier Science B.V. All rights reserved.

Control of single attosecond pulse generation from the reflection of a synthesized relativistic laser pulse on a solid surface

The influence of the carrier-envelope phase (CEP) of the driving laser pulse on the generation of single attosecond (as) pulses from surface harmonics by using the polarization gating technique is investigated in detail. It is found that the modulation depth of the high-order harmonic spectrum depends on the CEP, and a strong single 68 as pulse can be generated when the CEP is stable and has the proper value. The physical origin of the influence of the CEP is explained in terms of the oscillating mirror model. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2997342]

Spectral analysis and control to obtain sub-5 fs pulses by femtosecond filamentation

A spectral-filter method is numerically demonstrated to obtain sub-5 fs pulses by using femtosecond filamentation in fused silica. Instead of employing spectral phase compensation, by properly employing a high-pass filter to select the broadened high-frequency spectra that are located almost in phase in the tailing edge of the self-compressed pulses owing to self-steepening, as short as single-cycle pulses can be obtained. For instance, for an input pulse with a duration of 50 fs and energy 2.2 mu J, the minimum pulse duration can reach to similar to 4 fs (about 1.5 cycles) by applying a proper spectral filter. (C) 2008 Optical Society of America

Optimal feedback control of two-photon fluorescence in Coumarin 515 based on genetic algorithm

An optimal feedback control of two-photon fluorescence in the Coumarin 515 ethanol solution excited by shaping femtosecond laser pulses based on genetic algorithm is demonstrated experimentally. The two-photon fluorescence intensity can be enhanced by similar to 20%. Second harmonic generation frequency-resolved optical gating traces indicate that the optimal laser pulses are positive chirp, which are in favor of the effective population transfer of two-photon transitions. The dependence of the two-photon fluorescence signal on the laser pulse chirp is investigated to validate the theoretical model for the effective population transfer of two-photon transitions. The experimental results appear the potential applications in nonlinear spectroscopy and molecular physics. (c) 2005 Elsevier B.V. All rights reserved.

Multiple quasi-phase-matching for enhanced generation of selected high harmonics in aperiodic modulated fibers

A technique for enhanced generation of selected high harmonics in a gas medium, in a high ionization limit, is proposed in this paper. An aperiodically corrugated hollow-core fiber is employed to modulate the intensity of the fundamental laser pulse along the direction of propagation, resulting in multiple quasi-phase-matched high harmonic emissions at the cutoff region. Simulated annealing (SA) algorithm is applied for optimizing the aperiodic hollow-core fiber. Our simulation shows that the yield of selected harmonics is increased equally by up to 2 orders of magnitude compared with no modulation and this permits flexible control of the quasi-phase-matched emission of selected harmonics by appropriate corrugation. (c) 2007 Optical Society of America.

Optical two-dimensional SW-banyan network: Optical implementation, routing control, and determination of permissible permutations

A 2-D SW-banyan network is introduced by properly folding the 1-D SW-banyan network, and its corresponding optical setup is proposed by means of polarizing beamsplitters and 2-D phase spatial light modulators. Then, based on the characteristics and the proposed optical setup, the control for the routing path between any source-destination pair is given, and the method to determine whether a given permutation is permissible or not is discussed. Because the proposed optical setup consists of only optical polarization elements, it is compact in structure, its corresponding energy loss and crosstalk are low, and its corresponding available number of channels is high. (C) 1996 Society of Photo-Optical Instrumentation Engineers.

A phase-shifting vectorial-shearing interferometer with wedge plate phase-shifter

We present a novel phase-shifting vectorial-shearing interferometer with a wedge plate phase-shifter. The interferometer is based on a modified Mach-Zehnder configuration; the common-path nature makes it capable of testing the wavefront of a short coherence-length light source, such as a laser diode. Vectorial shear (shearing in the x and y directions simultaneously) in an arbitrary direction is introduced by inserting two wedge plates orthogonally in two arms, respectively. One of the wedge plates is split into two parts (parallel part and wedge part); phase shift is produced by moving the wedge part in contact along the parallel part. The moving distance for a 2 pi phase shift is a few millimetres in specific conditions. The wedge plate phase-shifter increases the moving distance for phase shift and makes the control of phase shift relatively easy. We also discuss the lateral shear error and phase shift errors induced by wedge plates. The lateral shear error is small enough to be ignored; the phase shift error is determined mainly by the wedge angle error. Lastly, we give the experimental results of phase-shifting interference fringes in vectorial shear mode.

Fabrication of fused silica phase gratings with inductively coupled plasma technology

Inductively coupled plasma (ICP) technology is a new advanced version of dry-etching technology compared with the widely used method of reactive ion etching (RIE). Plasma processing of the ICP technology is complicated due to the mixed reactions among discharge physics, chemistry and surface chemistry. Extensive experiments have been done and microoptical elements have been fabricated successfully, which proved that the ICP technology is very effective in dry etching of microoptical elements. In this paper, we present the detailed fabrication of microoptical fused silica phase gratings with ICP technology. Optimized condition has been found to control the etching process of ICP technology and to improve the etching quality of microoptical elements greatly. With the optimized condition, we have fabricated lots of good gratings with different periods, depths, and duty cycles. The fabricated gratings are very useful in fields such as spectrometer, high-efficient filter in wavelength-division-multiplexing system, etc..

Influences of phase shift on superresolution performances of annular filters

This paper investigates the influences of phase shift on superresolution performances of annular filters. Firstly, it investigates the influence of phase shift on axial superresolution. It proves theoretically that axial superresolution can not be obtained by two-zone phase filter with phase shift pi, and it gets the phase shift with which axial superresolution can be brought by two-zone phase filter. Secondly, it studies the influence of phase shift on transverse superresolution. It finds that the three-zone phase filter with arbitrary phase shift has an almost equal optimal transverse gain to that of commonly used three-zone phase filter, but can produce a much higher axial superresolution gain. Thirdly, it investigates the influence of phase shift on three-dimensional superresolution. Three-dimensional superresolution capability and design margin of three-zone complex filter with arbitrary phase shift are obtained, which presents the theoretical basis for three-dimensional superresolution design. Finally, it investigates the influence of phase shift on focal shift. To obtain desired focal shifts, it designs a series of three-zone phase filters with different phase shifts. A spatial light modulator (SLM) is used to implement the designed filters. By regulating the voltage imposed on the SLM, an accurate focal shift control is obtained.

Optimized phase pupil masks for extended depths of field

By properly designing a phase pupil mask to modulate or encode the optical images and then digitally restoring them, one can greatly extend the depth of field and improve image quality. The original works done by Dowski and Cathey introduce the use of a cubic phase pupil mask to extend the depth of field. The theoretical and experimental researches all verified its effectiveness. In this paper, we suggest the use of an exponential phase pupil mask to extend the depth of field. This phase mask has two variable parameters for designing to control the shape of the mask so as to modulate the wave-front more flexible. We employ an optimization procedure based on the Fisher information metric to obtain the optimum values of the parameters for the exponential and the cubic masks, respectively. A series of performance comparisons between these two optimized phase masks in extending the depth of field are then done. The results show that the exponential phase mask provide slight advantage to the cubic one in several aspects. (c) 2006 Elsevier B.V. All rights reserved.

Differing estrogen activities in the organic phase of air particulate matter collected during sunny and foggy weather in a Chinese city detected by a recombinant yeast bioassay

Total air suspended particles (PM 100) collected from an urban location near a traffic line in Wuhan, China, were examined for estrogen using a recombinant yeast bioassay. Wuhan, located at the central part of China, is the fourth biggest city in China with 7 million populations. Today, Wuhan has developed into the biggest city and the largest traveling center of central China, becoming one of the important bases of industry, education and research. Wuhan is right at the confluent point of Yangzi River, the third longest river in the world, and its largest distributary Hanjiang, with mountains and more than 100 takes in downtown area. Therefore, by its unique landscape, Wuhan has formed clear four seasons with relatively long winter and summer and short spring and autumn. Foggy weather usually happen in early spring. The yeast line used in this assay stably expresses human estrogen receptor-alpha. Weak but clear estrogenic activities were detected in the organic phase of crude extracts of air particle materials (APM) in both sunny and foggy weather by 0.19-0.79 mug E2/gPM(100) which were statistically significantly elevated relative to the blank control responding from 20% to 50% of the maximum E2 response, and the estrogenic activity was much higher in foggy weather than in sunny weather. The estrogenic activities in the sub-fractions from chromatographic separation of APM sampled in foggy days were also determined. The results indicated that the responses of the fractions were obviously higher than the crude extracts. Since there is no other large pollution source nearby, the estrogenic material was most likely from vehicle emissions, house heating sources and oil fumes of house cooking. The GC/MS analysis of the PM100 collected under foggy weather showed that there were many phenol derivatives, oxy-PAHs and resin acids which have been reported as environmental estrogens. These results of the analysis of estrogenic potency in sunny and foggy weather in a subtropical city of China indicate that further studies are required to investigate the actual risks for the associated health and atmospheric system. (C) 2004 Elsevier Ltd. All rights reserved.

Influence of dioxin and metal-contaminated sediment on phase I and II biotransformation enzymes in silver crucian carp

Several biochemical responses were measured in silver crucian carp (Carassius auratus gibelio) after exposure to sediments obtained from contaminated Ya-Er Lake, No, 1 pond, and an unpolluted reference site, Honglian Lake. After 1 week of exposure, a significant induction of the phase I biotransformation enzyme (ethoxylresorufin-o-deethylase, EROD) was found (83-fold of control), whereas the phase II biotransformation enzyme (glutathione S-transferase, GST) exhibited a slight, but significant induction (1,4-fold of control) after 4 weeks of exposure. The level of cellular glutathione in the liver was also slightly elevated after 4 weeks of exposure. The delayed response of GST to the contaminants indicates that the phase I and phase II biotransformation enzymes are regulated differently in fish. The results suggest that EROD is a sensitive bioindicator to assess the toxicity of dioxin-contamined sediment in the laboratory, (C) 1998 Academic Press.

Electrical control of dynamic spin splitting induced by exchange interaction as revealed by time-resolved Kerr rotation in a degenerate spin-polarized electron gas

Manipulation of the spin degree of freedom has been demonstrated in a spin-polarized electron plasma in a heterostructure by using exchange-interaction-induced dynamic spin splitting rather than the Rashba and Dresselhaus types, as revealed by time-resolved Kerr rotation. The measured spin splitting increases from 0.256 meV to 0.559 meV as the bias varies from -0.3 V to -0.6 V. Both the sign switch of the Kerr signal and the phase reversal of Larmor precessions have been observed with biases, which all fit into the framework of exchange-interaction-induced spin splitting. The electrical control of it may provide a new effective scheme for manipulating spin-selected transport in spin FET-like devices. Copyright (C) EPLA, 2008.

A simple route of morphology control and structural and optical properties of ZnO grown by metal-organic chemical vapour deposition

Employing the metal-organic chemical vapour deposition (MOCVD) technique, we prepare ZnO samples with different morphologies from the film to nanorods through conveniently changing the bubbled diethylzinc flux (BDF) and the carrier gas flux of oxygen (OCGF). The scanning electron microscope images indicate that small BDF and OCGF induce two-dimensional growth while the large ones avail quasi-one-dimensional growth. X-ray diffraction (XRD) and Raman scattering analyses show that all of the morphology-dependent ZnO samples are of high crystal quality with a c-axis orientation. From the precise shifts of the 2 theta. locations of ZnO (002) face in the XRD patterns and the E-2(high) locations in the Raman spectra, we deduce that the compressive stress forms in the ZnO samples and is strengthened with the increasing BDF and OCGF. Photoluminescence spectroscopy results show all the samples have a sharp ultraviolet luminescent band without any defects-related emission. Upon the experiments a possible growth mechanism is proposed.

Using different carrier gases to control AlN film stress and the effect on morphology, structural properties and optical properties

On the metalorganic chemical vapour deposition growth of AlN, by adjusting H-2+N-2 mixture gas components, we can gradually control island dimension. During the Volmer - Weber growth, the 2-dimensional coalescence of the islands induces an intrinsic tensile stress. Then, this process can control the in-plane stress: with the N-2 content increasing from 0 to 3 slm, the in-plane stress gradually changes from 1.5 GPa tensile stress to - 1.2GPa compressive stress. Especially, with the 0.5 slm N-2 + 2.5 slm H-2 mixture gas, the in-plane stress is only 0.1 GPa, which is close to the complete relaxation state. Under this condition, this sample has good crystal and optical qualities.