High-reflectivity non-periodic sub-wavelength gratings with small-angle beam-steering ability and its application in Fabry–Perot cavity

We report a high-reflectivity non-periodic sub-wavelength gratings (SWGs) mirror with small-angle beam-steering ability for reflect light. It presents a distinctive characteristic of flexibly controlling the width of oscillation optical field for the improved Fabry–Perot (F–P) cavity. We propose a detailed principle analysis of the improved cavity. By finding out a set of SWGs with the designed structural parameters, both high reflectivity (>?93%) and beam steering (1°) can be implemented. By setting beam-steering angle and cavity length, we can control the width of oscillation optical field in the improved cavity. Beam steering ability and property of controlling the oscillation width are numerically investigated by finite element method. Simulation results prove that cavity length and steering angle can effectively control the main width of oscillation optical field, and the width is linearly associated with the cavity length.     

水热法合成稀土氟化物材料YLiF4:Er,Tm,Yb的上转换发光特性

利用水热法合成了不同掺杂浓度Er^3 ,Tm^3 和Yb^3 的YLiF4材料,研究了Er^3 ,Tm^3 和Yb^3 在材料中的光吸收,以及在980nm红外光激发下样品的上转换发光特性。实验发现,在980nm激光激发下,光功率为数10mW,材料可以发出很强的白光。测量发现,蓝光来源于Tm^3 绿光来源于Er^3 ,而红光来源于Tm^3 和Er^3 的共同作用。通过分析输出光强与泵浦功率的双对数曲线,发现484nm蓝光发射,524和552nm绿光发射以及665nm红光发射均属于双光子过程,450nm蓝光和359nm紫外光属于三光子过程。分析发光机理属于协作敏化和声子辅助共振能量传递过程的结合。     

A Modified Approach for Calculating Dressed Quark Propagator at Finite Chemical Potential

Based on the rainbow approximation of Dyson-Schwinger equation and the assumption that the full inverse quark propagator at finite chemical potential is analytic in the neighborhood of μ = 1, it is proved that the dressed quark propagator at finite chemical potential μ can be written as G0^-1 [μ] =iγ·p↑-A（p↑-^2） ＋B（p↑-^2） with p↑-μ= （p↑-p4 ＋iμ）. From the dressed quark propagator at finite chemical potential in Munczek model the bag constant of a baryon and the scalar quark condensate are evaluated. A comparison with previous results is given.     

气相中Fe+催化CO与N2O循环反应的理论计算研究

采用密度泛函UB3 LYP/6-311+ G(2d)方法研究了Fe+在基态和激发态与CO与N2O反应的反应机理.全参数优化了反应势能面上各驻点的几何构型,用频率分析方法和内禀反应坐标(IRC)方法对过渡态进行了验证,并用UB3LYP/6-311++G(3df,3pd)、单点垂直激发等方法分别进行各驻点单点能校正,四重态和六重态反应势能面交叉点CP确定,计算结果表明,该反应为两步反应,且反应机理都为插入一消去反应,势能面上的两个交叉点能够有效降低反应的活化能,这在动力学和热力学上都是有利的.     

Rheological Properties of Template Polymerization Polyacrylamide Aqueous Solutions

In this work, the aqueous solution rheology properties of both partially hydrolyzed polyacrylamide (HPAM) and the template copolymer (TPAM) synthesized from acrylic acid (AA) and acrylamide (AM) were investigated using an advanced rheometer and viscometer. The results were correlated with the corresponding molecular structures of HPAM and TPAM, which were characterized by high-resolution nuclear magnetic resonance. It was found that the thickening ability of TPAM is much stronger than that of HPAM due to its unique microblocky structure, while the viscosity of TPAM was more sensitive to shear rate. Furthermore, the effect of polymer concentration was also tested in an oscillation shear mode. It showed that the characteristic relaxation time of TPAM was much higher than that of HPAM at the high concentrations. The research on salt-resistance properties showed that the viscosity retention of TPAM was similar to HPAM at the same NaCl concentration. But, unexpectedly, at the same CaCl₂ concentration the viscosity retention of TPAM was much lower than that of HPAM, indicating a poor divalent salt-resistance property.     

高能p-A碰撞Drell-Yan过程中的初态核效应

核遮蔽和能量损失效应是p-A碰撞中两种重要的初态核效应. 本文利用从轻子-原子核深度非弹性散射实验数据中抽取的束缚核子的部分子分布函数, 在色弦模型中研究了Drell-Yan双轻子对产生过程中的能量损失效应. 通过对FNAL E772和E866实验数据的χ²分析, 得到夸克在冷核中的能量损失率为－dE/dz=2.06GeV/fm. 这和该模型理论预言的结果(－dE/dz～2GeV/fm)一致. 通过将理论计算结果与实验数据进行比较, 发现考虑到能量损失后能很好的解释实验现象.     

Transmission Frequency Properties of Elastic Waves along a Hetero-Phononic Crystal Waveguide

We investigate the propagation properties of hetero-phononic crystal waveguides by the improved eigen-mode matching theory, which can be used at same time to calculate both the transmission （reflection） coefficient and band structure. The numerical results show that the transmission frequency range is the same as the common range for two uniform waveguides composing the hereto-system, and the gap of any composite waveguide is also the gap of the hetero-phononic crystals waveguide.     

非相干光纤激光组束中光栅参数的确定

光栅衍射效率是非相干光纤激光组束系统的关键,理论分析和数值仿真表明光栅衍射效率随着光栅频率和光栅厚度的减小而增大。全面综合考虑光栅频率应该选取在200mm-1和400mm-1之间,光栅厚度在1mm到2mm之间。同时提出了一种不等间隔方法提高系统总体衍射效率,该方法较等间隔条件下衍射效率提高了0.1651。     

Beam quality improvement and focused peak intensity measurement of an intense femtosecond Ti:sapphire laser system

Micro-lens arrays were adopted to homogenize the beam profile of 532-nm pumping laser for the main amplifier of an intense femtosecond, chirped pulse amplification (CPA) Ti:sapphire laser. Experimental measurements showed a great improvement of the near-field pattern of the CPA beam after the main amplifier and the size of the focal spot was improved from 2.7 times diffraction limitation (DL) to 1.6 DL.The spot size focused by an f/4 off-axis parabola (OAP) in the target chamber was measured to be 5.8μm (full-width at half-maximum (FWHM)), and a peak intensity of 2.6 × 1020 W/cm2 was obtained at the output power of 120 TW. Peak intensity exceeding 1021 W/cm2 or even 1022 W/cm2 can be expected with smaller f-number focusing configuration and wavefront correction.     

Analytical Solution for Single—Mode Time—Dependent Oscillator

Based on the general theory of time-dependent quantum transformation,we use the “time evolution operator” method to solve the single-mode time-dependent oscillator.