Tunable second harmonic generation by phase-modulated ultrashort laser pulses

We report on the generation of tunable light around 400?nm by frequency-doubling ultrashort laser pulses whose spectral phase is modulated by a sum of sinusoidal functions. The linewidth of the ultraviolet band produced is narrower than 1?nm, in contrast to the 12?nm linewidth of the non-modulated incident spectrum. The influence of pixellation of the liquid crystal spatial light modulator on the efficiency of the phase-modulated second harmonic generation is discussed.     

High order dispersion control for femtosecond CPA lasers

Taking advantage of the temperature dependence of the refractive index, an arrangement is proposed for thermal control of dispersion of a chirped pulse amplification (CPA) laser. A glass slab, inserted into the Fourier plane of a stretcher or a compressor, having a spatially varying temperature profile across the beam ensures continuous variation of the spectral phase shift of the pulses. Model calculations are carried out to investigate the feasibility of the arrangement. As a demonstration, simple temperature profiles are created which compensate for the material dispersion of the thermal slab. In a proof of principle experiment it is proved that changes of spectral phase of femtosecond pulses follow the spatially varying temperature profile of a BK7 slab inserted into the compressor of a CPA system. Such a thermal slab is lossless, has a large spectral range, introduces no pixellation and exhibits a high damage threshold. Since it is easy to build into either the stretcher or the compressor of existing CPA lasers, it may become a promising candidate for high order dispersion compensation of high-power femtosecond laser systems. PACS 42.65.Re; 42.79.-e; 42.60.By     

基于强度调制的新型偏振光谱仪调制器优化设计

强度调制是一种高光谱偏振信息获取新方法,可有效地解决现有测量法存在的不足。调制器是其中的关键硬件模块之一。从调制器实现偏振、光谱信息调制的基本原理入手,结合偏振、光谱信息的解调理论,提出了调制器参数优化设计方法,并对该方法进行了计算机数值模拟。结果表明:经过优化设计的调制器产生的各个载波信号的频率在光谱仪的采样带宽内均匀分布,有效地拓展了可测Stokes矢量元素谱的带宽范围,也为后续的偏振、光谱信息的高保真解调奠定了基础。     

Field form of perturbation theory for calculating the matrix elements of operators between the states of two degenerate atomic levels. I

It is shown that the calculation of the matrix elements between degenerate states of arbitrary atomicmolecular systems can be reduced to a calculation of the matrix elements for some auxiliary operator. The perturbation theory for this calculation can be given a field form, and its matrix elements can be expressed in terms of the contributions from special Feynman diagrams. The exact rules are formulated for constructing the contributions from these diagrams.     

ICP-AES法测定古代车师人肋骨中的痕量元素

近几十年来 ,古代人群的食谱研究已经成为现代科技考古学的一个重要组成部分 ,也是当前国际科技考古学研究领域的一项前沿性课题。人类骨骼的微量元素分析为重建古代居民的食谱提供了大量信息。本文用硝酸 盐酸消解样品 ,采用电感耦合等离子发射光谱仪 (ICP AES) ,在选定的最佳条件下 ,对新疆地区古代车师人肋骨中的Sr,Zn ,Ca ,Cu ,Mg,Fe ,Ba ,Mn等 8种痕量元素进行了测定 ,该方法采用一次溶样 ,多元素同时测定 ,回收率为 87 4 %～ 1 0 6 6 %之间。相对标准偏差为 0 5 %～ 3 3%。该方法简单 ,快捷可靠 ,适用于古代骨样品的测定 ,结果令人满意。其结果为考古学和人类学的研究提供了科学的依据。同时考察了不同酸度对分析结果的影响和共存元素间的相互干扰 ,此外还进行了精密度实验。     

Spectroscopic Mueller matrix polarimeter using four-channeled spectra

A Mueller matrix polarimeter acquired for four-channeled spectra is proposed. Both the polarizing and analyzing optics of this system consist of a linear polarizer and a high-order retarder. The polarizing elements can modulate the polarization states in the wavenumber space. By applying a Fourier transform method to a single-channeled spectrum, nine elements of the Mueller matrix can be deconvoluted without modifying the configuration of either the polarizing or analyzing optics. It is thus possible to determine the wavelength dependence of all the Mueller matrix elements from four-channeled spectra obtained using four different configurations for the polarizing and analyzing optics. The performance of this method is evaluated by measuring polarization properties, such as retardance, azimuthal angle, and linear diattenuation, from the obtained Mueller matrix in wavenumber space.     

Design of an inductively decoupled microstrip array at 9.4 T

By independent control of the phases and amplitudes of its elements, the microstrip transmission-line array can mitigate sample-induced RF non-uniformities, and has been widely used as the transceiver in parallel imaging applications. One major challenge in implementing the microstrip array is the reduction of mutual coupling among individual elements. The low-input impedance preamplifier is commonly used for the decoupling purpose. However, it is impractical in the transceiver array design. Although interconnecting capacitors can be utilized to reduce the mutual coupling, they only efficiently work for the neighbor elements. In addition, this approach is impractical at fields higher than 300 MHz, in which the required decoupling capacitance is commonly less than 0.5 pF. We propose a novel decoupling approach by using decoupling inductors in this study. Due to the fact that the decoupling inductance is independent of the resonant frequency, the microstrip arrays can be well decoupled at ultra-high fields. To verify the proposed approach, an eight-channel microstrip array is fabricated and tested at 9.4 T. For this prototype, couplings between elements are significantly reduced by using the interconnecting inductors. The phantom experiment shows that the inductively decoupled microstrip array has good parallel imaging performance.     

原子吸收和电感耦合等离子体发射光谱法测定某些重要的埃及植物

本文讨论了用原子吸收和电感耦合等离子体发射光谱法（ＩＣＰ－ＡＥＳ）测定经高压釜溶解的营养性埃及植物，如胡芦巴、甘草和莲座丛，并讨论了该法用于被消解植物样品中多元素日常分析的优点。这些样品具有较宽的元素含量范围，准确地测定这些营养性样品的主量和微量元素特别是有毒元素，对埃及人民的健康非常重要。ＩＣＰ－ＡＥＳ法同时也用于被视为尼罗河净化剂的水生风信子的分析。分析结果表明，该植物能够有效地吸收有毒元素。被研究的植物经高压釜溶解，其溶液经原子吸收和ＩＣＰ－ＡＥＳ法测定。作者对分析结果进行了对比，并阐明了二者之间的关系。     

Application of optimization algorithms to the design of diffractive optical elements for custom laser resonators

We report what we believe to be the first applications of numerical optimization algorithms to the design of diffractive elements that customize the fundamental mode profile of a laser system. Standard design techniques treat these elements as specific phase-conjugation devices, which leads to performance loss when they are quantized to permit fabrication. Numerical optimization can account for quantization of the element to increase the effective performance. Also, it is shown that allowing a slight increase in the intrinsic loss of the cavity can substantially increase the fidelity of the fundamental mode of the customized cavity. The good discrimination qualities of the mode-selection elements are shown to be unaffected by this process.     

Binary diffractive beam splitters with arbitrary diffraction angles

Diffractive optical beam splitters designed with iterative Fourier transform type algorithms can produce only certain diffraction angles given by the spatial frequencies used for the computations, which are multiples of a certain base spatial frequency. We have developed a design algorithm that overcomes this limitation and can be used to compute binary diffractive elements with arbitrary diffraction angles. The simulated and experimentally measured properties of optical elements producing beam arrays in circular arrangements are presented and discussed.     

Optimized quantization for diffractive phase elements by use of uneven phase levels

Many applications of diffractive phase elements involve the calculation of a continuous phase profile, which is subsequently quantized for fabrication. The quantization process maps the continuous range of phase values to a limited number of discrete steps. We present a new scheme with unevenly spaced levels for the design of diffractive elements and apply it to the design of intracavity mode-selecting elements. We show that this modified quantization can produce significantly better results than are possible with a regular or even the bias-phase-optimized quantization scheme that we reported here earlier. In principle this process can be employed to a greater or lesser extent in any quantization process, allowing the fabrication of diffractive elements with much improved performance.     

Flexible,phase-matched,linear receive arrays for high-field MRI in monkeys

High signal-to-noise ratios (SNR) are essential for high-resolution anatomical and functional MRI. Phased arrays are advantageous for this but have the drawback that they often have inflexible and bulky configurations. Particularly in experiments where functional MRI is combined with simultaneous electrophysiology, space constraints can be prohibitive. To this end we developed a highly flexible multiple receive element phased array for use on anesthetized monkeys. The elements are interchangeable and different sizes and combinations of coil elements can be used, for instance, combinations of single and overlapped elements. The preamplifiers including control electronics are detachable and can serve a variety of prefabricated and phase matched arrays of different configurations, allowing the elements to always be placed in close proximity to the area of interest. Optimizing performance of the individual elements ensured high SNR at the cortical surface as well as in deeper laying structures. Performance of a variety of arrangements of gapped linear arrays was evaluated at 4.7 and 7T in high-resolution anatomical and functional MRI.     

高压密封消化罐在光谱分析样品前处理中的应用

原了吸收光谱法是进行元素定量分析的快捷有效的方法,但固体试样溶解的不完全会对其分析测定的准确度带来很大影响。本文应用高压密封消化罐对电厂难溶的垢样进行消解,对消解条件进行了探索试验,确定了比较方便快捷、溶样完全的消解体系。并对垢样消解液中的一些常规元素作了相应的原子吸收光谱测定。     

A network approach for analysis of silencers with/without absorbent material

The object of this work is to establish a general approach that can analyze the performance of most of the silencers with/without sound absorbent material. Under the assumption of plane wave propagation, the transfer matrices between the two ends of straight pipe and two-duct perforated section are derived and taken as the basic elements. Based on the conditions of continuity of pressure and of mass velocity, the silencer is modeled as a network formed by the two basic elements. Then the sound attenuation characteristic of the silencers can be investigated. With this scheme the multiply connected acoustic filters can also be analyzed. Further, the porous sound absorbent material is also included in this scheme. The effect of sound absorption material on the performance of silencers is analyzed and discussed.     

新型便携式激光诱导击穿光谱系统综述

本文主要综述了国内外便携式激光诱导击穿光谱(LIBS)系统的研究进展和应用情况。目前该系统主要针对金属元素进行检测,对非金属等轻元素的定量分析需要较大能量的激光激发,但受限于激光器和光谱仪等组件体积的影响,研发便携式、高精度LIBS系统有较高难度。本文针对全元素检测便携设备的研发,利用限域和高压放电脉冲得到了增强的LIBS信号,降低了激光能量,从物理机理上给出了便携式LIBS设备研发的新方向。     

光致聚合物全混洗光互连全息元件的制备

采用只对红光敏感的光致聚合物全息干版通过 Ｈｅ－Ｎｅ ６３２ｎｍ激光波长两次掩膜曝光,在面积为３０ｍｍ × ６０ｍｍ的全息干版上制备出全息光学元件,并成功地用于全混洗光学互连的实验演示。全息光学元件的衍射效率为 ４０～ ５２％。     

Geometrical derivation of collective operators and paths in TDHF

It is first found that the intrinsic parity of an operator under time reversal and the interpretation of the operator as coordinate- or momentum-like in a TDHF calculation are not simply related. This is because the TDHF particle-hole basis is, in general, complex. The TDHF equation is then reformulated in the plane tangent to the Slater determinant manifold. This plane is spanned by the particle-hole basis. The particle-hole matrix elements of the Hartree-Fock Hamiltonian define the energy gradient vector in this tangent plane. This gradient is real when the Slater determinant is real. A TDHF calculation initiated from a real determinant induces, during the first infinitesimal time step, a purely imaginary variation of this determinant along the gradient. The gradient is thus identified with the matrix elements of a boost operator. The next infinitesimal time step defines, in turn, a displacement operator. These operators are retained as collective if the TDHF path is stable under changes of velocities. Various criteria are found for this stability condition. The theory cannot be applied straightforwardly to translations and rotations for there is no energy gradient to generate coordinate operators. Particle-hole matrix elements of boost operators can be obtained, however, by a multiplication by i of the matrix elements of displacement operators, since the latter are known explicitly. It is finally found that the rotation of a wavefunction is contradictory with angular momentum conservation in general. Conservation can be ensured by a rotation of the density only and a more elaborate evolution of the velocity field.     

The focus steering for high intensity focused ultrasound phased array based on real-time phase shift calculation

When time reversal technique is used in phased array high intensity focused ultrasound system to obtain self-adaptive focusing,it is needed to calculate the initial phases of the elements.Because of the frequency oscillation when the phase lock loop is initiated,different results are got in different segments using conventional methods.A method of calculating the phase difference was presented,that can display the changes of phase difference in real-time, and the steady phase differences can be regarded as the initial phases of the elements.The experimental results show that using the phase difference obtained by this method can get a better distribution of sound field in a certain spatial region.     

Multiple parton scattering in nuclei: twist-four nuclear matrix elements and off-forward parton distributions

Multiple parton scatterings inside a large nucleus generally involve higher-twist nuclear parton matrix elements. The gluon bremsstrahlung induced by multiple scattering depends not only on direct parton matrix elements but also on momentum-crossed ones, due to the Landau–Pomeranchuk–Migdal interference effect. We show that both types of twist-four nuclear parton matrix elements can be factorized approximately into the product of twist-two nucleon matrix elements in the limit of extremely large nuclei, A→∞, as assumed in previous studies. Due to the correlative nature of the twist-four matrix elements under consideration, it is actually the off-forward parton distributions that appear naturally in this decomposition, rather than the ordinary diagonal distributions probed in deeply-inelastic scattering. However, we argue that the difference between these two distribution classes is small in certain kinematic regimes. In these regions, the twist-four nuclear parton matrix elements are evaluated numerically and compared to the factorized form for different nuclear sizes within a schematic model of the two-nucleon correlation function. The nuclear size dependence is found to be A^4/3 in the limit of large A, as expected. We find that the factorization is reasonably good when the momentum fraction carried by the gluon field is moderate. The deviation can be more than a factor of 2, however, for small gluon momentum fractions, where the gluon distribution is very large.     

Positive Protocol for Quantum Teleportation Using Photon Polarization-Entangled W-Type State as the Quantum Channel

In this paper, we propose a protocol for teleporting the photon polarization-entangled state from a sender to a receiver in terms of optical elements. We show that the quantum teleportation protocol can be successfully realized with a certain probability by using a W state as the quantum channel. This protocol is based on optical elements, which are feasible with existing experimental technology.