Measuring temporal fluctuation on femtosecond scale in a random medium

We report an observation of femtosecond optical fluctuations of transmitted light when a coherent femtosecond pulse propagates through a random medium. They are a result of random interference among scattered waves coming from different trajectories in the time domain. Temporal fluctuations are measured by using cross-correlated frequency optical gating. It is shown that a femtosecond pulse will be broadened and distorted in pulse shape while it is propagating in random medium. The real and imaginary components of transmitted electric field are also distorted severely. The average of the fluctuated transmission pulses yields a smooth profile, probability functions show good agreement with Gaussian distribution. (c) 2007 Elsevier B.V. All rights reserved.

飞秒脉冲通过散射表面后的时域特性

从理论上和实验上对飞秒激光脉冲通过散射表面后的时域特性进行了研究分析。用频率分辨光学开关法对通过散射表面前后的飞秒脉冲进行了测量和对比。理论分析和实验结果表明, 由于散射表面对飞秒脉冲的散射导致飞秒脉冲的展宽和形状的畸变。输入脉冲在时间相关函数的半峰全宽为64 fs; 透射脉冲在时间相关函数半峰全宽的平均值为117 fs。对透射脉冲场的统计特性进行了讨论, 透射脉冲场实部和虚部的概率函数分布遵从高斯函数分布; 强度的概率分布遵从指数分布规律; 给出了入射飞秒脉冲强度的自相关函数分布和飞秒时域散斑场强度的互相关函数分布的实验结果, 并且对二者的时间相关函数进行了讨论。

Subwavelength imaging with two symmetrical interfaces by dielectric-tube photonic crystals

As distinct from coated photonic crystals, in this paper we propose a novel one that is made of dielectric tubes arranged in a close-packet square lattice. Without metallic cores, this structure is low-loss and convenient to fabricate. A left-handed frequency region is found in the second band by dispersion characteristic analysis. Without inactive modes for the transverse electric mode, negative refraction and subwavelength imaging are demonstrated by the finite-difference time-domain simulations with two symmetrical interfaces, i.e. Gamma X and Gamma M.

Comment on: Computation of the optical trapping force using an FDTD based technique

In this comment, problems associated with an oversimplified FDTD based model used for trapping force calculation in recent papers "Computation of the optical trapping force using an FDTD based technique" [Opt. Express 13, 3707 (2005)], and "Rigorous time domain simulation of momentum transfer between light and microscopic particles in optical trapping" [Opt. Express 12, 2220 (2004)] are discussed. A more rigorous model using in Poynting vector is also presented.

用于高重复频率热容主振荡功率放大器激光系统的波前检测技术

高重复频率热容主振荡功率放大器(MOPA)激光系统的工作过程一般只持续几秒至几十秒,在此过程中系统输出光束的波前畸变是动态变化的。采用环路径向剪切干涉(CRWSI)技术对高重复频率热容MOPA系统波前畸变的变化过程进行检测,并对系统的总体结构进行了设计。搭建了一个简化的实验系统,采用平凹透镜来代替光放大器产生波前畸变,并由此对环路径向剪切干涉仪的测量精度进行了验证。结果表明,实验测量结果与理论计算值之间的峰值误差为7.8%(0.02λ)。

PSII放氧复合物的光组装及相关蛋白结构与功能研究

本文主要研究了一系列具有不同配位环璄的锰化合物与去锰PSII颗粒的光组装过程;其次，应用太赫兹时域光谱技术对锰稳定蛋白PsbO蛋白的结构与功能进行了研究。主要结果如下： 1. 选择了一组单核、锰中心原子为二价、与羧基氧和氮配位的锰化合物与去锰光系统II颗粒进行了重组研究。研究结果表明，锰化合物中锰原子和氮原子的配位连接是影响电子传递恢复和放氧复合物重组效率的重要因素。锰化合物中锰原子与氮原子的配位，促进了锰原子与PSII脱辅基蛋白上的氨基酸残基进行光配位。33 kDa蛋白的加入显著提高光组装放氧活性，33 kDa蛋白的柔性构象有助于锰簇接受体积大的分子，并提高其稳定性，从而促进PSII反应中心锰簇的光组装。 2. 选择了一组拥有相同配体、锰中心原子价态不同的锰化合物与去锰PSII 颗粒进行重组。三个锰价态为＋2，＋3，＋4价的锰化合物均表现出较高的恢复电子传递和放氧活性的能力，但锰与配体氧原子共价连接的锰化合物恢复电子传递和放氧活性的能力的很差，Mn-O连接阻碍WOC的重组。研究结果表明，锰化合物恢复电子传递活性和放氧活性的能力也受其中锰原子的价态及其它结构因素的影响。锰价态较低的锰化合物比锰价态较高的锰化合物更容易向PSII反应中心提供电子。锰化合物恢复电子传递和放氧活性的因素是不同的。锰化合物作为有效电子供体的效率与其螯合环数成反比，但配体的大小不是影响锰化合物重组放氧活性的主要因素。 3. 应用太赫兹时域光谱技术结合荧光光谱技术，研究了锰稳定蛋白PsbO在与金属离子作用及单个氨基酸被修饰后其构象变化和低频振动模的变化。实验结果显示，该蛋白上唯一的色氨酸对整个蛋白构象至关重要，它的改变引起整个蛋白分子低频振动模发生明显改变。此外，太赫兹时域光谱结果显示，PsbO可能含有钙结合位点。太赫兹时域光谱技术在研究蛋白构象变化，尤其是金属离子诱导的构象变化方面是相当灵敏的。

Acute effects of microcystins on the transcription of antioxidant enzyme genes in crucian carp Carassius auratus

Recent evidences suggested that oxidative stress may play a significant role in the pathogenesis of MCs toxicity. In the present study, the acute effects of microcystins on the transcription of antioxidant enzyme genes were investigated in liver of crucian carp i.p.-injected with 50 mu g MC-LReq per kg body weight (BW). We reported the cDNA sequences for four kinds of antioxidant enzyme (GSH-PX, CAT, Cu/Zn SOD, and GR) genes, and evaluated the oxidant stress induced by MCs through analyzing the transcription abundance of antioxidant enzyme genes using real-time PCR method. The time-dependent change of relative transcription abundance and expression of the antioxiclant enzyme genes were determined at 1, 3, 12, 24, and 48 h. The transcription abundance varied among antioxiclant enzymes, with GSH-PX and GR down-regulation, and CAT and SOD significantly upregulation. Based on these data, we tentatively concluded that the oxidant stress was induced by MCs, and caused the different response of the antioxiclant enzyme genes. (c) 2008 Wiley Periodicals, Inc.

Mode Simulation for Midinfrared Microsquare Resonators With Sloped Sidewalls and Confined Metals

EQUILATERAL-TRIANGLE; MU-M; LASERS; MICROLASERS; MICRODISK Abstract: Mode characteristics for midinfrared microsquare resonators with sloped sidewalls and confined metal layers are investigated by finite-difference time-domain (FDTD) techniques. For a microsquare with a side length of 10 mu m, the mode quality (Q)-factors of 8329, 4772, and 2053 are obtained for TM5,7 mode at wavelength 7.1 mu m by three-dimensional FDTD simulations, as the tilting angles of the side walls are 90 degrees, 88 degrees, and 86 degrees, respectively. Furthermore, microsquare resonators laterally surrounded by SiO2 and metal layers are investigated by the two-dimensional FDTD technique for the metal layers of Au, Ti-Au, Ag-Au, and Ti-Ag-Au, respectively.

Investigation of mode radiation loss for microdisk resonators with pedestals by FDTD technique

Mode radiation loss for microdisk resonators with pedestals is investigated by three-dimensional (3D) finite-difference time-domain (FDTD) technique. For the microdisk with a radius of 1 mu m, a thickness of 0.2 mu m, and a refractive index of 3.4, on a pedestal with a refractive index of 3.17, the mode quality (Q) factor of the whispering-gallery mode (WGM) quasi-TE7,1 first increases with the increase of the radius of the pedestal, and then quickly decreases as the radius is larger than 0.75 mu m. The mode radiation loss is mainly the vertical radiation loss induced by the mode coupling between the WGM and vertical radiation mode in the pedestal, instead of the scattering loss around the perimeter of the round pedestal. The WG M can keep the high Q factor when the mode coupling is forbidden.

Enhancement of quality factor for TE whispering-gallery modes in microcylinder resonators

The enhancement of quality factor for TE whispering-gallery modes is analyzed for three-dimensional microcylinder resonators based on the destructive interference between vertical leakage modes. In the microcylinder resonator, the TE whispering-gallery modes can couple with vertical propagation modes, which results in vertical radiation loss and low quality factors. However, the vertical loss can be canceled by choosing appropriate thickness of the upper cladding layer or radius of the microcylinder. A mode quality factor increase by three orders of magnitude is predicted by finite-difference time-domain simulation. Furthermore, the condition of vertical leakage cancellation is analyzed.

Mode characteristics of metallically coated square microcavity connected with an output waveguide

Mode characteristics of a square microcavity with an output waveguide on the middle of one side, laterally confined by an insulating layer SiO2 and a p-electrode metal Au, are investigated by two-dimensional finite-difference time-domain technique. The mode quality (Q) factors versus the width of the output waveguide are calculated for Fabry-Peacuterot type and whispering-gallery type modes in the square cavity. Mode coupling between the confined modes in the square cavity and the guided modes in the output waveguide determines the mode Q factors, which is greatly influenced by the symmetry behaviors of the modes. Fabry-Peacuterot type modes can also have high Q factors due to the high reflectivity of the Au layer for the vertical incident mode light rays. For the square cavity with side length 4 mu m and refractive index 3.2, the mode Q factors of the Fabry-Peacuterot type modes can reach 10(4) at the mode wavelength of 1.5 mu m as the output waveguide width is 0.4 mu m.

Analysis of coupled microcircular resonators coupled to a bus waveguide with high output efficiency

Coupled microcircular resonators tangentially coupled to a bus waveguide, which is between the resonators, are numerically investigated by the finite-difference time-domain technique. For symmetrically coupled microcircular resonators with refractive index of 3.2, radius of 2 mu m, and width of the bus waveguide of 0.4 mu m, a mode Q factor of the order of 105 is obtained for a mode at the frequency of 243 THz. An output coupling efficiency of as high as 0.99 is calculated for a mode with a Q factor ranging from 10(3) to 10(4). The mode Q factor is 2 orders larger than that of the modes confined in a single circular resonator tangentially coupled to the same bus waveguide. Furthermore, the high Q traveling modes in the coupled microcircular resonators are suitable for optical single processing.

Investigation on multiple-port microcylinder lasers based on coupled modes

Microcylinder resonators with multiple ports connected to waveguides are investigated by 2D finite-difference time-domain (FDTD) simulation for realizing microlasers with multiple outputs. For a 10 mu m radius microcylinder with a refractive index of 3.2 and three 2 mu m wide waveguides, confined mode at the wavelength of 1542.3 nm can have a mode Q factor of 6.7 x 10(4) and an output coupling efficiency of 0.76. AlGaInAs/InP microcylinder lasers with a radius of 10 mu m and a 2 mu m wide output waveguide are fabricated by planar processing techniques. Continuous-wave electrically injected operation is realized with a threshold current of 4 mA at room temperature, and the jumps of output power are observed accompanying a lasing mode transformation.

Directional emission InP/GaInAsP square-resonator microlasers

InP/GaInAsP square-resonator microlasers with an output waveguide connected to the midpoint of one side of the square are fabricated by standard photolithography and inductively-coupled-plasma etching technique. For a 20-mu m-side square microlaser with a 2-mu m-wide output waveguide, cw threshold current is 11 mA at room temperature, and the highest mode Q factor is 1.0 X 10(4) measured from the mode linewidth at the injection current of 10 mA. Multimode oscillation is observed with the lasing mode wavelength 1546 nm and the side-mode suppression ratio of 20 dB at the injection current of 15 mA. (C) 2008 Optical Society of America

Enhancement of the far-field output power and the beam properties of plasmonic very small aperture lasers

The properties of plasmonic very small aperture lasers are shown: these integrate surface plasmon structures with very small aperture lasers. The transmission field can be confined to a spot of subwavelength width in the far field, and according to the finite difference time domain simulation results the focal length of the spot can be modulated using different ring periods. Scanning of the subwavelength gating in the far field has been realized numerically. Such a device can be used with a high-resolution far-field scanning optical microscope.