激光冷却和困禁中性原子

目前利用激光来冷却和困禁中性原子的技术已取得激动人心的进展，通过使用廉价的二极管激光器和蒸汽室收集器，有效地降低了困禁原子的复杂性和高成本，在零点的μＮ温度下，可得到１０＾１１个原子／ｃｍ＾３的原子密度，本文介绍了有关激光冷却与困禁技术，讨论了其现实应用，频率标准→基本物理性质研究。     

相干布居囚禁现象用于原子频标

在Λ型三能级原子系统模型的基础上,采用半经典的密度矩阵方法分析了87Rb气体的相干布居囚禁现象。数值模拟结果显示,当两束相干激光频率差等于87Rb原子的两个基态超精细结构子能级频率差时,87Rb气体具有相干暗线和相干微波辐射的特性。它们可以作为相干布居囚禁原子频标的鉴频物理基础。最后简要分析了两种相干布居囚禁原子频标的各自特点和实验装置结构。     

CPT原子钟的微型原子泡加工工艺综述

原子泡是CPT（相干布居囚禁）原子钟物理部分的主体,对于微型原子钟而言,传统的吹玻璃法已不再适用,必须用新的技术和方法来设计加工原子泡。介绍了利用MEMS（微机电系统）技术结合吹玻璃法、空心光纤嵌套法和MEMS方法加工微型原子泡的工艺以及碱金属原子和缓冲气体的几种常见的注入方法。     

从CPT原子钟到光钟

简要介绍了新型CPT（Coherent population trapping，相干布局囚禁）原子频标及光频标的基本原理和研究进展。被动型CPT铷原子钟物理部分的目前体积可控制在100cm^3以内，功耗1W左右，其稳定度为4×10^-11τ^-1/2（τ为测量取样的时间间隔）。CPT原理的铯原子频标的物理部分体积减小到1cm^3，功率减小到30mW，稳定度为6×10^-10τ^-1/2，成为当今体积最小、功耗最低的原子钟。随着飞秒激光梳状发生器技术的发展，已将传统的谐波光频链的体积从几间实验室缩小到1．2×1．0m^2的光学平台上，它与光频测量技术的结合，使微波频标与光频标联系起来，建立了光钟，它的稳定性可以从现在的10^-16的水平提高到10^-18乃至10^-22水平，成为当前最精密的时间计量仪器。     

一种CPT频标小体积低功耗温控电路的研制

为满足小型、低功耗被动型相干布居囚禁（coherent population trapping,CPT）原子频标的需要,利用开关电源芯片设计并研制了一种基于电源芯片的温控电路。实验结果表明：与常用温控电路相比,该电路控温能力与其相当,功耗降低25％,体积减少一半。因此,该电路特别适合小型、低功耗CPT原子频标的需要,也为其他需要小型、低功耗温控电路的应用提供了一种可选方案。     

激光参量对CPT铷原子钟稳定度影响的数值分析

为具体分析激光参量对相干布居囚禁(CPT)原子钟的稳定度性能的影响,在(-型三能级原子系统模型的基础上,采用半经典密度矩阵方法,数值模拟计算了不同激光参量对CPT铷原子钟共振谱线信号的影响,并给出了比较分析.结果显示:两束激光强度的不对称对CPT钟信号强度的影响很大,而激光频率失谐对CPT钟信号影响较小;此外,当激光强度不对称与频率失谐同时存在时,荧光信号谱出现不对称,微波辐射信号发生频移.     

锶原子光钟磁光阱磁场及其控制电路设计

由于锶原子光钟两级冷却对磁光阱磁场有不同的要求,为减少磁场转换时原子的逃逸,需在短时间内以一定的时序控制变换磁场。对反赫姆霍兹线圈设计的一般理论进行了讨论,为锶原子光钟的两级冷却设计了相应的磁场,并制作了转换磁场的发生控制装置。该装置主要包括控制电路、保护电路2部分。测量得到通过线圈的电流受控于输入信号,符合实验要求。     

分子云的热平衡

本文介绍了各种对分子云热平衡作出贡献的加热和冷却机制,如分子或原子的辐射冷却(或加热),尘埃-气体碰撞加热和引力坍缩加热等等。并且讨论了如何确定不同类型分子云的热平衡温度。     

铷原子频标小型化发展现状

铷原子频标使用最广泛,小型化是其最重要的发展趋势。微波腔小型化、电子线路数字化以及附加特殊功能是铷原子频标小型化的主要技术手段。相干布居囚禁(CPT)频标是一种可以做到芯片级的新型原子频标。目前相干布居囚禁频标的技术方案有:传统方案,物理系统采用MEMS(micro-electro-mechanical system)[0]技术的方案和整机采用MEMS[0]技术的方案。实现小型化后的原子频标将会迎来蓬勃发展的前景。     

国外原子时频最新进展

概述了传统原子频标的现状，以及新型原子频标和国际原子时的研究进展，介绍了为适应高精度新型频标和国际原子时的比对需要而开展的远程时频传递技术。     

Instructions for authors

正Research in Astronomy and Astrophysics publishes original research papers and reviews on all branches of astronomy and astrophysics.Reviews are by invitation only.Important new results that require rapid publication can be submitted as a Letter(Letters must be restricted in length to 6 printed pages).Authors who submit a paper are expected to be able to certify that the paper is original work,     

Research in Astronomy and Astrophysics CONTENTS

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Instructions for authors

正Research in Astronomy and Astrophysics publishes original research papers and reviews 011 all liranchcs of astronoiriy and astrophysics.Reviews arc by invitation only.Important new results that require rapid publication can be submitted as a Letter(Letters must be restricted in length     

Alkali and halogen chemistry in volcanic gases on Io

We use chemical equilibrium calculations to model the speciation of alkalis and halogens in volcanic gases emitted on Io. The calculations cover wide temperature (500-2000 K) and pressure (10⁻⁶ to 10⁺¹ bars) ranges, which overlap the nominal conditions at Pele (T=1760 K, P=0.01 bars). About 230 compounds of 11 elements (O, S, Li, Na, K, Rb, Cs, F, Cl, Br, I) are considered. The elemental abundances for O, S, Na, K, and Cl are based upon observations. CI chondritic elemental abundances relative to sulfur are used for the other alkalis and halogens (as yet unobserved on Io). We predict the major alkali species in Pele-like volcanic gases and the percentage distribution of each alkali are LiCl (73%), LiF (27%); NaCl (81%), Na (16%), NaF (3%); KCl (91%), K (5%), KF (4%); RbCl (93%), Rb (4%), RbF (3%); CsCl (92%), CsF (6%), Cs (2%). Likewise the major halogen species and the percentage distribution of each halogen are NaF (88%), KF (10%), LiF (2%); NaCl (89%), KCl (11%); NaBr (89%), KBr (10%), Br (1%); NaI (61%), I (30%), KI (9%). We predict the major halogen condensates and their condensation temperatures at P=0.01 bar are NaF (1115 K), LiF (970 K); NaCl (1050 K), KCl (950 K); KBr (750 K), RbBr (730 K), CsBr (645 K); and solid I₂ (200 K). We also model disequilibrium chemistry of the alkalis and halogens in the volcanic plume. Based on this work and our prior modeling for Na, K, and Cl in a volcanic plume, we predict the major loss processes for the alkali halide gases are photolysis and/or condensation onto grains. Their estimated photochemical lifetimes range from a few minutes for alkali iodides to a few hours for alkali fluorides. Condensation is apparently the only loss process for elemental iodine. On the basis of elemental abundances and photochemical lifetimes, we recommend searching for gaseous KCl, NaF, LiF, LiCl, RbF, RbCl, CsF, and CsCl around volcanic vents during eruptions. Based on abundance considerations and observations of brown dwarfs we also recommend a search of Io's extended atmosphere and the Io plasma torus for neutral and ionized Li, Cs, Rb, and F.     

The climatic and physiographic controls of the eastern Mediterranean over the late Pleistocene climates in the southern Levant and its neighboring deserts

Modern-day synoptic-scale eastern Mediterranean climatology provides a useful context to synthesize the diverse late Pleistocene (60–12 ka) paleohydrologic and paleoenvironmental indicators of past climatic conditions in the Levant and the deserts to its south and east. We first critically evaluate, extract, and summarize paleoenvironmental and paleohydrologic records. Then, we propose a framework of eastern Mediterranean atmospheric circulation features interacting with the morphology and location of the southeast Mediterranean coast. Together they strongly control the spatial distribution of rainfall and wind pattern. This cyclone–physiography interaction enforces the observed rainfall patterns by hampering rainfall generation south and southeast of the latitude of the north Sinai coast, currently at 31°15′.The proposed framework explains the much-increased rains in Lebanon and northern Israel and Jordan as deduced from pollen, rise and maintenance of Lake Lisan, and speleothem formation in areas currently arid and semiarid. The proposed framework also accounts for the southward and eastward transition into semiarid, arid, and hyperarid deserts as expressed in thick loess accumulation at the deserts' margins, dune migration from west to east in the Sinai and the western Negev, and the formation of hyperarid (< 80 mm yr^− 1) gypsic–salic soils in the southern Negev and Sinai. Our climatic synthesis explains the hyperarid condition in the southern Negev, located only 200–250 km south of the much-increased rains in the north, probably reflecting a steeper rainfall gradient than the present-day gradient from the wetter Levant into its bordering southern and eastern deserts.At present, the rainiest winter seasons in Lebanon and northern and central Israel are associated with more frequent (+ 20%), deeper Cyprus Lows traversing the eastern Mediterranean at approximately the latitude of southern Turkey. Even these wettest years in northern Israel do not yield above average annual rainfall amounts in the hyperarid southern Negev. This region is mainly influenced by the Active Red Sea Troughs that produce only localized rains. The eastern Mediterranean Cyprus Lows also produce more dust storms and transport higher amounts of suspended dust to the loess area than any other atmospheric pattern. Concurrent rainfall and dust are essential to the late Pleistocene formation of the elongated thick loess zone along the desert northern margin. Even with existing dust storms, the lack of rain and very sparse vegetation account for the absence of late Pleistocene loess sequences from the southern Negev and the formation of hyperarid soils.When the north Sinai coast shifted 30–70 km northwest due to last glacial global sea level lowering, the newly exposed coastal areas supplied the sand and dust to these active eastern Mediterranean cyclones. This enforced the latitude of the northern boundary of the loess zone to be directly due east of the LGM shoreline. This shift of coast to the northwest inhibited rainfall in the southern Levant deserts and maintained their hyperaridity. Concurrently, frequent deep eastern Mediterranean Cyprus Lows were funneled along the northern Mediterranean increasing (probably doubling) the rains in central and northern Israel, Lebanon, southwestern Syria and northern Jordan. These storms and rains formed lakes, forests, and speleothems only a short distance north of the deserts in the southern Levant.     

Study on the Stressed Mirror Polishing with a Continuous Polishing Machine for Large Aperture Off-axis Aspheric Mirrors

A special stressed annular polishing technique is proposed to mill the off-axis aspheric sub-mirrors of a large segmented mirror with an annular polishing machine. Based on the basic principle of stressed annular polishing technique, a set of special stressing mechanisms are designed to convert milling the aspheric surfaces of sub-mirrors with different off-axis distances into milling the spherical surfaces with identical radii of curvature, so that they can be pol- ished simultaneously on a continuous polishing machine. It took about contin- uous 40 hours to polish a scaled-down mirror of the planning Chinese Future Giant Telescope (CFGT) using this technique. This mirror has the 330 mm di- ameter, 3.6 m off-axis distance, and the 21.6 m radius of curvature, and its max- imum asphericity is 16 micron. The experiment shows that this method has a high effciency, suits batch manufacturing, especially the batch manufacturing of aspheric sub-mirrors of the segmented primary mirror of an extremely large aperture telescope.     

Active hot star shells

Interferometry in the visible provides milliarcsecond spatial resolution and thus has been used for studying the circumstellar environment of active hot stars. In this paper I will illustrate how the visibility modulus and phase can be used to better constrain the physics of Be disks through results from the VLA, the MkII and the GI2T interferometers. I will insist on the importance and the potential of coupling high angular resolution with high spectral resolution to the study of Be shells. Finally I will present a possible study of the circumstellar disk of Be stars using the VLTI. This revised version was published online in July 2006 with corrections to the Cover Date.     

Fitting X-ray Afterglow Light curves of Gamma-ray Bursts by Using the Magnetar Energy Injection Model

The central compact object for some gamma-ray bursts (GRBs) may be a strongly magnetized millisecond pulsar. It can inject energy to the outer shock of the GRB by through the magnetic dipole radiation, and therefore causes the shallow decay of the early afterglow. Recently, from a large number of GRB X-ray afterglows observed by Swift/XRT(X-ray telescope), it is revealed that many of them exhibit the shallow decay about 10²∼10⁴ s after the burst prompt emission. We have fitted the X-ray afterglow light curves of 11 GRBs by using the energy injection model of a magnetar with the rotation period in the millisecond order of magnitude. The obtained result shows the validity and universality of the magnetar energy injection model in explaining the shallow decay of afterglows, and simultaneously provides some constraints on the magnetic field strength and rotation period of the central magnetar.     

我国新一代VLBI数字基带转换器研制进展

数字化是目前设备研制发展的趋势,介绍了中国科学院上海天文台利用超大规模集成电路结合软件无线电技术,自主研发的我国新一代VLBI数字基带转换器(Chinese Data Acquisition System,简称CDAS).文中描述了设备的工作原理及其组成,并以VLBI观测实验数据证明其可行性.与原有的模拟设备(Anal...