Quantum cascade surface-emitting photonic crystal laser

We combine photonic and electronic band structure engineering to create a surface-emitting quantum cascade microcavity laser. A high-index contrast two-dimensional photonic crystal is used to form a micro-resonator that simultaneously provides feedback for laser action and diffracts light vertically from the surface of the semiconductor surface. A top metallic contact allows electrical current injection and provides vertical optical confinement through a bound surface plasmon wave. The miniaturization and tailorable emission properties of this design are potentially important for sensing applications, while electrical pumping can allow new studies of photonic crystal and surface plasmon structures in nonlinear and near-field optics.     

Room-temperature ultraviolet nanowire nanolasers

Room-temperature ultraviolet lasing in semiconductor nanowire arrays has been demonstrated. The self-organized, <0001> oriented zinc oxide nanowires grown on sapphire substrates were synthesized with a simple vapor transport and condensation process. These wide band-gap semiconductor nanowires form natural laser cavities with diameters varying from 20 to 150 nanometers and lengths up to 10 micrometers. Under optical excitation, surface-emitting lasing action was observed at 385 nanometers, with an emission linewidth less than 0.3 nanometer. The chemical flexibility and the one-dimensionality of the nanowires make them ideal miniaturized laser light sources. These short-wavelength nanolasers could have myriad applications, including optical computing, information storage, and microanalysis.     

Transform-limited, narrow-linewidth lasing action in organic semiconductor microcavities

Lasing action in organic vertical-cavity surface-emitting laser (OVCSEL) structures is demonstrated. Optically pumped OVCSELs with an active layer composed of a thin-film organic semiconductor tris-(8-hydroxyquinoline) aluminum (Alq3) doped with DCM laser dye produced very narrow linewidth (0.2 +/- 0.1 angstrom), high-power (3 watts) emission that could be varied in different devices from orange to red. The efficient energy transfer from Alq3 to DCM results in a threshold input energy of 300 microjoules per square centimeter. An operational lifetime >10(6) laser pulses was achieved for a device operated well above threshold in atmosphere. The linewidths above threshold are Fourier transform-limited and could potentially be narrowed further.     

High-gain backward lasing in air

The compelling need for standoff detection of hazardous gases and vapor indicators of explosives has motivated the development of a remotely pumped, high-gain air laser that produces lasing in the backward direction and can sample the air as the beam returns. We demonstrate that high gain can be achieved in the near-infrared region by pumping with a focused ultraviolet laser. The pumping mechanism is simultaneous resonant two-photon dissociation of molecular oxygen and resonant two-photon pumping of the atomic oxygen fragments. The high gain from the millimeter-length focal zone leads to equally strong lasing in the forward and backward directions. Further backward amplification is achieved with the use of earlier laser spark dissociation. Low-divergence backward air lasing provides possibilities for remote detection.     

呼和浩特市南郊大气污染源调查的分析

呼和浩特市南郊大气污染源调查的分析杨秋林，郭玲，杨性恺，席延钰（内蒙古农牧学院基础课部，呼和浩特市，０１００１８）摘要调查了呼市南郊大气污染源的现状，分析了主要污染源和污染物，提出了对呼市南郊大气污染的防治对策和建议。关键词大气，大气污染，污染源，污...     

Coherent soft x-ray generation in the water window with quasi-phase matching

We demonstrate enhanced generation of coherent light in the "water window" region of the soft x-ray spectrum at 4.4 nanometers, using quasi-phase-matched frequency conversion of ultrafast laser pulses. By periodically modulating the diameter of a gas-filled hollow waveguide, the phase mismatch normally present between the laser light and the generated soft x-ray light can be partially compensated. This makes it possible to use neon gas as the nonlinear medium to coherently convert light up to the water window, illustrating that techniques of nonlinear optics can be applied effectively in the soft x-ray region of the spectrum. These results advance the prospects for compact coherent soft x-ray sources for applications in biomicroscopy and in chemical spectroscopy.     

Ultrafast X-ray Pulses from Laser-Produced Plasmas

A high-temperature plasma is created when an intense laser pulse is focused onto the surface of a solid. An ultrafast pulse of x-ray radiation is emitted from such a plasma when the laser pulse length is less than a picosecond. A high-speed streak camera detector was used to determine the duration of these x-ray pulses, and computer simulations of the plasmas agree with the experimental results. Scaling laws predict that brighter and more efficient x-ray sources will be obtained by the use of more intense laser pulses. These sources can be used for time-resolved x-ray scattering studies and for the development of x-ray lasers.     

图书馆室内环境改良研究

装修产生的有害物质严重污染室内环境, 近期出现的雾霾天气更引起人们对室内空气质量的关注, 图书馆作为重要的公共场所存在多种污染源, 这些污染源可分为尘埃、有害生物、有害气体、电磁辐射和噪声, 研究室内环境改良策略和技术, 采用科学的通风、防尘、采光和装修策略控制污染源, 降低污染程度, 结合图书馆实际工作经验和环保领域新兴技术提出图书馆室内环境改良技术, 主要有除尘技术、空气净化技术、灭菌消毒技术、室内绿化技术。     

Visualization of dislocation dynamics in colloidal crystals

The dominant mechanism for creating large irreversible strain in atomic crystals is the motion of dislocations, a class of line defects in the crystalline lattice. Here we show that the motion of dislocations can also be observed in strained colloidal crystals, allowing detailed investigation of their topology and propagation. We describe a laser diffraction microscopy setup used to study the growth and structure of misfit dislocations in colloidal crystalline films. Complementary microscopic information at the single-particle level is obtained with a laser scanning confocal microscope. The combination of these two techniques enables us to study dislocations over a range of length scales, allowing us to determine important parameters of misfit dislocations such as critical film thickness, dislocation density, Burgers vector, and lattice resistance to dislocation motion. We identify the observed dislocations as Shockley partials that bound stacking faults of vanishing energy. Remarkably, we find that even on the scale of a few lattice vectors, the dislocation behavior is well described by the continuum approach commonly used to describe dislocations in atomic crystals.     

Emission of coherent THz radiation from superconductors

Compact solid-state sources of terahertz (THz) radiation are being sought for sensing, imaging, and spectroscopy applications across the physical and biological sciences. We demonstrate that coherent continuous-wave THz radiation of sizable power can be extracted from intrinsic Josephson junctions in the layered high-temperature superconductor Bi2Sr2CaCu2O8. In analogy to a laser cavity, the excitation of an electromagnetic cavity resonance inside the sample generates a macroscopic coherent state in which a large number of junctions are synchronized to oscillate in phase. The emission power is found to increase as the square of the number of junctions reaching values of 0.5 microwatt at frequencies up to 0.85 THz, and persists up to approximately 50 kelvin. These results should stimulate the development of superconducting compact sources of THz radiation.     

6MF-30便携式风力灭火机气动噪声分析

便携式风力灭火机是我国用于森林消防的重要设备,然而,其噪声会严重影响操作人员的生理和心理健康。本文采用FLUENT气动噪声场仿真和噪声测试试验相结合的方法,确定风力灭火机的主要气动噪声源,同时提出灭火机降噪优化的设计建议。结果表明:二维模型和大涡模拟(配合FW-H方程)结合的方法可以用于风力灭火机气动噪声的仿真,但在仿真过程中需考虑消声器的影响;风力灭火机主要气动噪声源为叶轮和涡舌,风筒噪声对其总噪声贡献较小;建议增加导流器等,以降低风力灭火机工作过程中操作人员的耳旁噪声。      

Creation and manipulation of three-dimensional optically trapped structures

An interferometric pattern between two annular laser beams is used to construct three-dimensional (3D) trapped structures within an optical tweezers setup. In addition to being fully translatable in three dimensions, the trapped structure can be rotated controllably and continuously by introducing a frequency difference between the two laser beams. These interference patterns could play an important role in the creation of extended 3D crystalline structures.     

New laser source technology

Over the past 5 to 8 years several new laser sources have been developed as a result of R & D efforts stimulated by a growing number of laser applications. Four families of new devices-semiconductor diod laser arrays, free electron lasers, rare gas halide excimer sources, and several new tunable solid-state lasers-show particular promise.     

北京地区灰霾化学特性研究进展

近年来北京及周边地区灰霾发生频繁,对其形成气象条件、气候效应及模型预报等方面的研究迅速兴起.灰霾的形成是由气象因素和大气污染物共同决定的,以不同人为活动为代表的不同污染物排放源,为灰霾的形成提供了本地源.而污染物的大尺度迁移、扩散,又构成了更大空间尺度城市群落的气溶胶区域污染.笔者分别综述了北京地区的灰霾天气现状、北京灰霾化学组成特征、来源及区域性特点,并在此基础上指出,明确和区分北京及周边地区灰霾化学特性的时空变异特征及不同排放源的相对贡献量,进一步发展和应用新型分析测试手段,开展多学科综合研究,是北京地区灰霾研究和控制的重要发展趋势.     

减排对泰州市环境空气质量变化趋势的影响

[目的]掌握泰州市减排措施实施后空气质量现状及其变化趋势。[方法]对2013~2015年泰州市空气质量监测数据进行系统分析,研究减排对泰州市环境空气质量的影响。[结果]受减排影响显著,空气质量有逐步好转的趋势。SO_2、PM_(10)、PM_(2.5)和CO年均浓度分别下降3.8%、12.9%、20.8%和30.2%,PM_(10)和PM_(2.5)下降幅度较大,NO_2和O_3年均浓度分别上升19.2%、19.3%。[结论]能源结构变化、污染源综合整治是改善空气质量的关键。     

A route to the brightest possible neutron source?

We review the potential to develop sources for neutron scattering science and propose that a merger with the rapidly developing field of inertial fusion energy could provide a major step-change in performance. In stark contrast to developments in synchrotron and laser science, the past 40 years have seen only a factor of 10 increase in neutron source brightness. With the advent of thermonuclear ignition in the laboratory, coupled to innovative approaches in how this may be achieved, we calculate that a neutron source three orders of magnitude more powerful than any existing facility can be envisaged on a 20- to 30-year time scale. Such a leap in source power would transform neutron scattering science.     

Megacity emissions and lifetimes of nitrogen oxides probed from space

Megacities are immense sources of air pollutants, with large impacts on air quality and climate. However, emission inventories in many of them still are highly uncertain, particularly in developing countries. Satellite observations allow top-down estimates of emissions to be made for nitrogen oxides (NO(x) = NO + NO(2)), but require poorly quantified a priori information on the NO(x) lifetime. We present a method for the simultaneous determination of megacity NO(x) emissions and lifetimes from satellite measurements by analyzing the downwind patterns of NO(2) separately for different wind conditions. Daytime lifetimes are ~4 hours at low and mid-latitudes, but ~8 hours in wintertime for Moscow. The derived NO(x) emissions are generally in good agreement with existing emission inventories, but are higher by a factor of 3 for the Saudi Arabian capital Riyadh.     

激光技术在农作物检测中的应用进展

激光技术现已成功应用于农作物组分检测、长势监测、病虫害监测、农药残留检测、田间杂草识别及辅助精细农业操作等方面,并日益凸显出检测准确、快速、低成本等优势,在农作物检测中应用较多的激光技术主要包括激光漫反射技术、激光诱导荧光光谱技术和激光拉曼光谱技术。笔者重点介绍了这3种技术用于农作物检测的原理、系统构成、应用进展和发展趋势。     

中国水产品产量结构变化特征研究

水产品产量结构是反映渔业产业内部结构和外部资源变化的重要指示器。利用1997～2010年水产品产量数据,从生产水域、生产方式和产品种类三个不同角度,对我国水产品产量结构变化特征进行了分析。结果表明:(1)从生产水域来看,海水产品仍是水产品市场供给的主要来源,预计到2014年淡水产品将取代海水产品地位,成为市场主力;(2)从生产方式来看,自2006年海水养殖比重超过海水捕捞比重后,标志着渔业完全实现"以养为主"的发展战略,淡水养殖产量的比重最高,已超过40%;(3)从产品种类来看,淡水鱼类、海水贝类和海水鱼类是水产品产量结构的主要品种。分析认为淡水渔业将会成为未来较长时期我国水产品供给的主要来源。建议制定淡水渔业发展战略,科学指导淡水渔业产业发展,促进淡水渔业可持续发展。     

Proposed square spiral microfabrication architecture for large three-dimensional photonic band gap crystals

We present a blueprint for a three-dimensional photonic band gap (PBG) material that is amenable to large-scale microfabrication on the optical scale using glancing angle deposition methods. The proposed chiral crystal consists of square spiral posts on a tetragonal lattice. In the case of silicon posts in air (direct structure), the full PBG can be as large as 15% of the gap center frequency, whereas for air posts in a silicon background (inverted structure) the maximum PBG is 24% of the center frequency. This PBG occurs between the fourth and fifth bands of the photon dispersion relation and is very robust to variations (disorder) in the geometrical parameters of the crystal.