使用Fabry—Perot干涉腔稳频的GaAlAs激光器(英文)

GaAlAs激光器的激射频率被锁定于Fabry-Perot干涉腔上。在锁定之后其激射频率的涨落已被大大地降低。所测得的频率稳定度(对Fabry-Perot干涉腔中心频率的跟踪稳定度)如下:其中第1个稳频系统为5×10~(-12)(1s)、1.5×10~(-12)(10s)、1.2×10~(-12)(100s);而第2个稳频系统为8×10~(-12)(1s)、2×10~(-12)(10s)、1.8×10~(-12)(100s)。     

分子泛频谱稳频半导体激光器

利用一阶导数和三阶导数稳频技术，成功地将AlGaAs半导体激光的频率锁定到H2O分子的泛频吸收谱线上，测得1秒和10秒取样时间的频率稳定度分别为1.5-10^-10和4.0×10^-11。     

光抽运铯束频标的初步实验结果

本文报告北京大学光抽运铯束频标的初步实验结果,其频率稳定度的阿仑方差已达到1.2×10~(-11)/τ~(1/2),与常规商品铯束频标的频率稳定度相当。实验中采用了偏置-饱和吸收式频率锁定技术,将半导体激光器频率稳定地锁定在适当的铯原子跃迁频率上。这是一种简便、经济而且十分可靠的激光频率锁定方法,实验中用它锁定激光频率达一百多个小时。     

镱离子光钟的多波长数字PID激光稳频系统

针对镱离子光钟实验中激光冷却并操控离子时,激光器频率漂移影响原子钟系统的问题,基于数字PID控制方法,设计了一种新的多通道频率-数字信号转换稳频方法,将多路多波长激光频率锁定在波长计的参考频率上。对激光器锁定前和锁定后的频率进行一定时长的数据采集及数据对比,激光频率漂移由800 MHz控制在± 0.8 MHz,激光频率稳定度由9.29 × 10^-10@1 s优化至2.79 × 10^-10@1 s,频率千秒稳达到3.85 × 10^-12。该系统简单、易实现,具有小型化、适应性强的优点。     

以半导体激光器为光源的准直研究

对半导体激光器的准直装置、温度变化对准直精度的影响、温度控制方法作了论述。试验表明,采用半导体激光器作准直光源,准直的稳定性可达到1×10~(-6)。     

外腔半导体激光器探测1.5μm波段乙炔分子谱线及稳频

用外腔半导体激光器观测到１．５μｍ波段乙炔（Ｃ２Ｈ２）分子１０条吸收谱线，对各谱线中心波长进行准确定标；对１．５３１５９μｍ的吸收线性质做了初步研究。对外腔半导体激光器的频率实现了分子诺线稳频，在１．５３１５９μｍ吸收谱线上，锁定后激光器的频率变化≤±２ＭＨｚ     

半导体激光器用铷D2线光电流谱稳频

本文报导了用铷原子７８００Ａ光电流谱来稳定半导体激光器的工作，在光电流谱线的中部发现了有利于稳频的凹陷，将半导体激光器频率锁定在凹陷的中央，估算的频率稳定度为１ＭＨｚ。     

基于声光偏频法的激光频率无调制锁定

为了进一步提高1.5 μm波段激光器的频率稳定性,利用声光调制器(AOM)的频移特性使激光发生频移,将乙炔(~(12)C_2H_2)v_1+v_3带的P9支吸收峰作为参考频率,通过两条频移的吸收谱线产生类色散鉴频曲线,实现对外腔半导体激光器的无调制频率锁定.实验中把以前直接对激光器的调制转移到声光调制器上,避免了直接调制所引入的额外噪声,通过闭环锁定,50 s内典型的频率起伏达到5.8 MHz以内,激光器的频率起伏较自由运转时明显得到抑制,实现了激光频率的稳定.     

~85Rb原子D_2线饱和吸收谱稳定半导体激光频率

用780nm AlGaAs半导体激光器和差分放大技术,观测了~(85)Rb原子D_2线(5S_(1/2)-5P_(3/2))B分量(5S_(1/2),F=2→5P_(3/2),F=1,2,3)的消多普勒饱和吸收谱。利用一阶导数和三阶导数稳频技术,实现了对AlGaAs半导体激光的稳频,对于1s和10s的取样时间,频率稳定度可达10~(-10)～10~(-11)。     

4.3μm荧光稳频的CO_2激光器及其频率稳定度的拍频测量

本文描述利用4.3μm荧光饱和共振稳定CO_2激光器频率的基本原理和装置。测量了4.3μm荧光兰姆凹陷的宽度和深度,确定了其一阶、三阶微分信号与调制宽度、吸收室温度等参数的关系。拍频测量结果表明,其频率稳定度为2×10~(-10)(10s),复现性优于1×10~(-9)。     

Insertion of triangulated surfaces into a meccano tetrahedral discretization by means of mesh refinement and optimization procedures

In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method.     

Certification Institutions Expected to Update and Transfer Information on Present Standards

Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……     

Flow calorimeter for enthalpy increment measurements on condensed gases

A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.     

Refrigerators Enter a New Era of Health Preservation Frestech initiates the establishment of China's first standard for household sterilization refrigerators

On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……     

Optimum-Simulation von Ernteprozessen

Zusammenfassung Bei der Gestaltung von Ernteprozessen — beispielsweise des Prozesses Mähdrusch, Körnertransport und -abnahme — als transportverbundene Fließarbeitsverfahren mit mindestens zwei verschiedenen Arbeitsmitteln gibt es einen großen Optimierungsspielraum. Solche Prozesse sind mehrstufige Bedienungsprozesse mit gemischter Anordnung der Bedienungseinrichtungen. Außerdem besitzen sie stark ausgeprägte räumliche Aspekte. Es wird vor allem gezeigt, welche Merkmale solcher Prozesse in Simulationsmodellen abgebildet sein müssen, welche Zielgrößen in Abhängigkeit von welchen Einflußgrößen unter Berücksichtigung welcher Prozeßbedingungen ermittelt werden sollten und wie der Bewertungsprozeß zur Ermittlung der gewünschten Informationen gestaltet werden muß.     

A study of centrifugal cast high boron high speed steel

In the present study a high‐boron high speed steel (HSS) roll material was designed. Many expensive alloy elements have been substituted by cheap boron alloy, and high‐boron high speed steel roll has been manufactured by centrifugal casting method. The microstructures, mechanical properties and wear resistance of centrifugal casting high‐boron high speed steel roll have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD) analysis, hardness test, impact test and wear test. The results indicated that the solidification microstructures of high‐boron high speed steel roll consisted of M₂(B,C), (W,Mo)₂(B,C), M₃(B,C), M₂₃(B,C)₆ type borocarbides and martensite, a small amount of retained austenite. Borocarbides were continuously distributed over the grain boundary. After quenching from 1050 °C, local broken network appeared in partial borocarbides, and fine secondary borocarbide precipitated from the matrix. After tempering from 525 °C, the amount of precipitated borocarbide increased significantly. After heat treatment, the hardness of high‐boron high speed steel roll excelled 60 HRC, and its impact toughness excelled 8.0 J/cm². The single groove steel rolling amount of high‐boron high speed steel rolls increases by 500% than that of bainite cast iron roll, when the rolls are used in K₁ mill housing of bar mill.     

Thixotropy of Systems with Shear Thinning and Plastic Flow Behavior

The definition of the thixotropy is a decrease in viscosity with time in shear and a subsequent recovery of viscosity after the shear deformation is removed.We ...     

Brainstorming for ISO Strategy 2016-2020

正Responding to ISO’s appeal for survey for the to-be-developed ISO Strategy Plan for 2016-2020,SAC hosted a special workshop over the needs and comments of various fi elds on June 8 in Beijing.The workshop was attended by ISO President-elect and Ansteel General Manager Zhang Xiaogang,SAC Vice-Administrator Yu Xinli,and 30 experts from     

CNAS Passes APLAC's PTP Review

正The review group of Asia Pacific Laboratory Accreditation Cooperation(APLAC)carried out a 4-day peer review of the proficiency testing provider(PTP)for China National Accreditation Service for Conformity Assessment(CNAS)from July 28 to 31,2014.CNAS passed the PTP review with excellent performance.Two senior peer reviewers of APLAC made a comprehensive,rigorous and detailed review of CNAS’s PTP accreditation activities,and made the on-spot inspection of the review groups in Shanghai and Shenzhen respectively.