698nm窄线宽激光器研究进展

窄线宽激光器在铯原子喷泉钟、光钟以及时间频率传递等方面有着重要的作用。主要介绍中国科学院国家授时中心开展的工作波长为698 nm窄线宽激光器的研究进展。实验中采用两级稳频方法将激光锁到初稳腔和高稳腔。通过第一级稳频,激光线宽为1.1 kHz;目前已初步实现了第二级稳频。通过逐渐优化第二级稳频,可以实现Hz量级线宽激光。     

657nm外腔半导体激光器的实现

对一种Littman-Metcalf外腔结构半导体激光器的实现过程作了报道.利用这种结构的光反馈特性,使原来自由运转时波长在660nm附近的半导体激光器在常温下能够调节到657nm附近,并且把激光线宽从原来的30MHz压窄到100kHz左右,连续调节范围大约为10GHz.这种窄线宽的激光器将用在钙原子Ramsey光谱的实验中.     

利用窄线宽激光测量锶原子束速率分布

利用多普勒频移效应,通过线宽2MHz窄线宽激光与锶原子束在大角度作用下的荧光信号分析,测量了锶原子束速率分布。比较和分析表明,理论结果与实验结果符合较好。     

基于LabwindowsCVI的外腔半导体激光器数字稳频系统设计

为抑制外腔半导体激光器频率漂移,提高频率稳定性,提出一种数字稳频方法。该方法采用数据采集卡,基于LabwindowsCVI语言实现数字锁相放大模块获得稳频误差信号,通过此信号控制压电陶瓷电压,将852 nm外腔半导体激光器的频率锁在铯原子谱线上,实现20 s频率稳定度8.7×10-11。该数字稳频方法降低了人力成本,易升级和修改,具有移植性好和用户界面友好等优点。     

Sr原子电磁感应透明效应相关理论研究

从理论上研究了Sr原子系统中电磁感应透明（EIT）效应及其伴随的Kerr非线性效应。计算表明,将一级冷却得到的Sr冷原子粘团作为光场与原子相互作用的EIT介质,用较弱的耦合光可以得到一个非常窄的EIT窗口和较强的Kerr非线性效应。该研究结果为实现689nm激光器的线宽压窄及应用EIT效应进行。Sr玻色子冷原子光钟研究提供了理论参考。     

基于光纤麦克尔逊干涉仪的激光稳频研究1

光纤不等臂干涉仪是光纤稳频式激光器的重要部分,它使激光频率的波动反映为干涉仪输出的相位扰动,从而利用干涉仪作为参考可以对激光的频率噪声进行抑制。通过对实验中采用的麦克尔逊光纤干涉仪进行研究,经过理论推导和实验测量,结果表明：采用光纤不等臂干涉仪的方法对激光进行稳频,可以使激光低频处的频率噪声得到较大的抑制,并且激光稳频过程中反馈环路的控制带宽主要受限于光纤不等臂干涉仪的时间延迟之差。     

超导稳频振荡器微波腔的优化设计

为应用于超导稳频振荡器,针对目前已有的超导微波腔进行了优化设计。综合考虑超导腔的表面电磁场、机械加工及表面处理等因素,决定采用圆柱形腔。所设计的圆柱形微波腔工作模式为TM010,直径为50 mm,高度为26.5 mm,频率为4.5 GHz。优化束管尺寸以减小对超导腔电磁场模式的影响,所设计的束管直径为10 mm,长度为50 mm。     

铷原子频标中微波功率频移的研究及其控制方法

针对铷原子频标中微波功率频移的传统解释与实验现象不相符合的矛盾，曾提出以ＡＣＺｅｅｍａｎ效应为核心的新解释．本文以实验检验了该解释，尤其是ＡＣＺｅｅｍａｎ效应频移公式的正确性，实验结果与理论相符合；最后探讨了控制微波功率频移的方法。     

基于液晶相位可变延迟器频率调谐外腔半导体激光器

利用液晶相位可变延迟器慢轴折射率随外加电压变化的特性,研制了一台用液晶进行频率调谐的分布反馈(DFB,distributed feedback)外腔半导体激光器。液晶DFB外腔激光器输出激光线宽为475 kHz,液晶电压变化1.6 V(0.5～2.1 V)时,激光频率变化为7 GHz,覆盖了Cs原子D2线的全部饱和吸收谱线。在实现外腔半导体激光器方法中,应用液晶调相较应用压电陶瓷(PZT)改变腔长,其具有调谐电压低,回程误差小,并可以消除机械稳定性差等特点。     

低漂移外腔半导体激光器驱动电路的设计

针对自制的852nm外腔半导体激光器,设计了一套低漂移的外腔半导体激光器驱动电路。通过恒温控制模块控制激光二极管的温度,高稳恒流源驱动激光二极管,外腔温控电路用于外腔的温度控制,高压恒压源控制外腔中压电陶瓷的长度。阐述了各部分电路的工作原理,并为降低激光器的频率漂移对电路做了优化。测试结果显示,1h内激光器频率漂移降为15MHz。     

A method to measure the mirror reflectivity of a prime focus telescope

We have developed a method to measure the mirror reflectivity of telescopes. While it is relatively easy to measure the local reflectivity of the mirror material, it is not so straightforward to measure the amount of light that it focuses in a spot of a given diameter. Our method is based on the use of a CCD camera that is fixed on the mirror dish structure and observes simultaneously part of the telescope’s focal plane and the sky region around its optical axis. A white diffuse reflecting disk of known reflectivity is fixed in the telescopes focal plane. During a typical reflectivity measurement the telescope is directed to a selected star. The CCD camera can see two images of the selected star, one directly and another one as a spot focused by the mirror on the white disk. The ratio of the reflected starlight integrated by the CCD from the white disk to the directly measured one provides a precise result of the product of (mirror area × mirror reflectivity).     

LAMOST子镜镀膜研究进展

对大口径光学/红外天文望远镜而言,为保障其稳定高效运行,镜面镀膜是重要的维护环节之一.镀膜质量的好坏直接影响镜面光学反射率的高低,也严重影响到天文望远镜的成像质量、观测效率.国家重大科技基础设施—大天区面积多目标光纤光谱天文望远镜(Large Sky Area Multi-Object Fiber Spectroscopic Telescope, LAMOST,又名郭守敬望远镜)自2009年6月通过国家竣工验收并逐步投入巡天观测,目前已进入第2个5 yr巡天计划阶段,取得近两千万的光谱产出和大批高显示度的科学成果. LAMOST共拥有24块施密特改正镜子镜和37块球面主镜子镜,为了确保在野外恶劣观测环境下镜面反射率维持在较高水平,每年要对大批子镜进行镀膜.主要介绍了镀膜需求、镀膜设备,并基于大量实验和多年的完善探索出一套可行的镀膜工艺流程,确保了LAMOST子镜极高的镀膜质量.镀膜后子镜平均反射率高达90%以上,满足了LAMOST光谱巡天的镜面反射率要求.     

The Ferrara hard X-ray facility for testing/calibrating hard X-ray focusing telescopes

We will report on the current configuration of the X-ray facility of the University of Ferrara recently used to perform reflectivity tests of mosaic crystals and to calibrate the experiment JEM–X aboard Integral. The facility is now located in the technological campus of the University of Ferrara in a new building (named LARIX laboratory= ̳LARge ̳Italian ̳X-ray facility) that includes a tunnel 100 m long with, on the sides, two large experimental rooms. The facility is being improved for determining the optical axis of mosaic crystals in Laue configuration, for calibrating Laue lenses and hard X-ray mirror prototypes.     

Infrared reflectance spectroscopy on thin films: Interference effects

Laboratory simulations of processes on astronomical surfaces that use infrared reflectance spectroscopy of thin films to analyze their composition and structure often ignore important optical interference effects which often lead to erroneous measurements of absorption band strengths and give an apparent dependence of this quantity on film thickness, index of refraction and wavelength. We demonstrate these interference effects experimentally and show that the optical depths of several absorption bands of thin water ice films on a gold mirror are not proportional to film thickness. We describe the method to calculate accurately band strengths from measured absorbance spectra using the Fresnel equations for two different experimental cases, and propose a way to remove interference effects by performing measurements with P-polarized light incident at Brewster's angle.     

Rings of Uranus: Not so thick,not so black

The optical thickness of the rings of Uranus has been thoroughly measured by many stellar occultations. However, we show that the optical thickness so obtained is larger by an extinction efficiency factor of 2 than the fractional area physically filled by particles which is commonly used to infer both particle reflectivity and particle size. By neglecting this factor, previous work has overestimated particle packing density and therefore underestimated individual particle reflectances and sizes (as well as overestimated collision frequencies). This has led to concern as to why the ring particles seemed unusually black and small. We present new estimates of particle reflectance which include both this effect and an improved radiative transfer treatment, and show that the ring particles, while still quite dark, are no longer mysteriously so. Particle sizes, while not strongly constrained, could easily lie in the macroscopic size range characteristic of other planetary rings.     

主动光学─新一代大望远镜的关键技术

对主动光学技术在现代天文光学望远镜中的作用和工作原理作了较全面的介绍和评论。结合作者近十年的工作对薄镜面主动光学技术和拼接镜面主动光学技术的各个关键部分,如波前检测、波前拟合、校正力的确定、共焦和共面的检测作了较详细且深入的讨论和评述．也介绍了我国目前正在研制的同时采用薄镜面主动光学和拼接镜面主动光学技术的大天区面积多目标光纤光谱望远镜的主动光学系统。     

Ground-based radar observations of Titan: 2000-2008

We have observed Titan with the Arecibo Observatory’s 12.6 cm wavelength radar system during the last eight oppositions of the Saturn system with sufficient sensitivity to characterize its scattering properties as a function of sub-Earth longitude. In a few sessions the Green Bank Telescope was used as the receiving instrument in a bistatic configuration to boost sub-radar track length and integration time. Radar echo spectra have been obtained for a total of 92 viewing geometries with sub-Earth locations scattered through all longitudes and at latitudes between 7.6°S and 26.3°S, close to the maximum southern excursion of the sub-Earth track. We find Titan to have globally average radar albedos at this wavelength of 0.161 in the opposite circular polarization sense as that transmitted (OC) and 0.074 in the same sense (SC), giving a polarization ratio SC/OC of 0.46. These values are intermediate between lower reflectivity rocky surfaces and higher reflectivity clean icy surfaces. The variations with longitude in general mirror the surface brightness variations seen through the infrared atmospheric windows. Xanadu Regio’s radar reflectivity and polarization ratio are higher than the global averages, and suggest that its composition is relatively cleaner water ice or, possibly, some other material with low propagation loss at radio wavelengths. For all echo spectra most of the power is in a broad diffuse component but with a specular component whose strength and narrowness is highly variable as a function of surface location. For all data we fit a sum of the standard Hagfors scattering law describing the specular component and an empirical diffuse radar scattering model to extract bulk parameters of the surface. Many areas exhibit very narrow specular reflections implying terrain that are quite flat on centimeter to meter scales over spans of tens to perhaps hundreds of kilometers. The proportion of spectra showing these narrow specular echoes has fallen significantly over the observational time span, indicating either a latitudinal effect related to terrain differences or changing surface conditions over the past several years. A few radar tracks, especially those from the 2008 session, overlap some high resolution Cassini RADAR imagery swaths to allow a direct comparison with terrain.     

ASO-S/FMG稳像系统的柔性支撑摆镜设计与仿真

全日面矢量磁像仪(Full-disk vector MagnetoGraph, FMG)是先进天基太阳天文台(Advanced Space-based Solar Observatory, ASO-S)的主载荷之一,摆镜作为FMG稳像系统的重要组成部分,其力学性能是决定载荷观测指标的重要一环,需要对其进行仿真.设计了一种侧面固定的柔性支撑镜体结构,通过调整垫片厚度,可以得到由弹性压片提供的不同大小支持力.为了确定合理的支持力范围,建立3种不同参数模型,使用有限元软件对摆镜模型进行了在轨无重力环境的静力学仿真以及摆镜摆动频率为100 Hz、摆幅为±0.1 mrad时的动力学仿真,并进一步分析了地面有重力试验环境对面形的影响.仿真结果表明所设计的摆镜机构模型均满足通光口径内静态和动态的面形波峰波谷差(PeakValley, PV)小于1/10波长,面形均方根误差(Root Mean Square, RMS)小于1/40波长的光学系统要求,地面有重力环境不会对面形产生显著影响.在仿真结果的基础上,对其中一种模型进行加工装配和实际测试,测试结果表明摆镜结构设计合理,仿真计算结果有效.     

Thermalizing a telescope in Antarctica – analysis of ASTEP observations

The installation and operation of a telescope in Antarctica represent particular challenges, in particular the requirement to operate at extremely cold temperatures, to cope with rapid temperature fluctuations and to prevent frosting. Heating of electronic subsystems is a necessity, but solutions must be found to avoid the turbulence induced by temperature fluctuations on the optical paths. ASTEP 400 is a 40cm Newton telescope installed at the Concordia station, Dome C since 2010 for photometric observations of fields of stars and their exoplanets. While the telescope is designed to spread star light on several pixels to maximize photometric stability, we show that it is nonetheless sensitive to the extreme variations of the seeing at the ground level (between about 0′′.1 and 5′′) and to temperature fluctuations between –30°C and –80 °C. We analyze both day‐time and night‐time observations and obtain the magnitude of the seeing caused by the mirrors, dome and camera. The most important effect arises from the heating of the primary mirror which gives rise to a mirror seeing of 0′′.23 K^–1. We propose solutions to mitigate these effects. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)