Principle demonstration of the phase locking based on the electro-optic modulator for Taiji space gravitational wave detection pathfinder mission

Weak-light phase locking is a key technology for Taiji space gravitational wave detection and its pathfinder mission. Previously, the phase locking was achieved by a complicated technique, which controls the frequency of the laser via a piezo-electric actuator (kHz range or more) and a temperature actuator (sub-Hz range). We propose an easy phase-locking strategy, which is based on the electro-optic modulator (EOM). Compared with the traditional way, this strategy only needs to modulate the driven voltage of the EOM, and the frequency bandwidth can cover all ranges. An experiment is also established to prove the feasibility of the method. The results show that the noises are &lt;80 mu rad/Hz(1/2) in frequencies from 0.2 to 1 Hz, and the thermal drift is the main noise source in our recent system. (C) 2018 Society of Photo-Optical Instrumentation Engineers (SPIE)</p

Method of Soil Quality Evaluation Under Different Land Use in Southern Ningxia Mountain Area

目前关于土壤质量评价的方法很多,综合了多变量指标克立格法、土壤质量综合评分法和土壤相对质量评价法各种方法的优点,也融入了本地区的土壤特性研究,制定了有区域特色的层次分析法;确立了隶属函数及其中的参数,因而实现了原始数据的归一化处理;同时也解决了利用主成分分析法如何决定各评价因子的权重分配问题

Features of Soil Organic Carbon Under Different Land Use in Mountain Area of Southern Ningxia

在宁夏固原上黄试验区,对灌木林地、农地、天然草地、果园和人工草地5种土壤的化学性质进行了分析,探讨了土地利用方式对土壤有机碳的影响。结果表明1表层土壤有机碳含量表现为天然草地&gt;灌木林地&gt;农地&gt;人工草地&gt;果园;2灌木林地和果园土壤有机碳含量随土层加深而变化幅度较小,而天然草地、人工草地和农地随土层加深而递减的幅度较大;30～20cm天然草地和灌木林地的有机碳密度普遍偏高,而农地、果园和人工草地则均较低;而20～40cm和0～40cm的土层内土壤有机碳密度相比之下灌木林地、农地和天然草地相差不大,而果园和人工草地相对较低

Constant amplitude modulation heterodyne interferometry

Laser interferometer with picometer precision is a key technology in the space gravitational wave detection. Many interferometry strategies have been put forward for the multiple purposes in the past 10 yr. We propose a new interferometry method, called constant amplitude modulation (CAM) heterodyne interferometry. Differently, the CAMprovides an optical pilot tone (OPT) for the noise correction theme. Compared with the analog pilot tone, the OPT can record and correct more noises, such as the analog to digital converter sampling jitter, the photodetector noise and the analog front-end noise. From the discussion, the modulated depth phi(modulate) = 1.375 rad and the power ratio of the beam split n = 0.432 are the best choice for the CAM-modulated parameter. Moreover, a simulated case has been implemented for the verification of the CAM strategy. Therefore, the CAM gives us another excellent choice in the optical design of the interferometer. (c) 2022 Optica Publishing Grou

空间引力波探测中的绝对距离测量及通信技术

空间引力波探测任务中,由于干涉臂臂长的巨大差异,激光频率不稳定噪声成为系统最大的噪声源之一。需采用Pound-Drever-Hall锁腔、锁臂和TDI(Time Delay Interferometer)技术三级联合,将此噪声压制到10~(-6)Hz~(1/2)量级,才能使得频率噪声低于散粒噪声。而实现TDI技术需要准确测量卫星间的绝对距离和星间通信。本文以空间引力波探测中的绝对距离测量和通信技术为背景,详细阐述此项技术的实现原理和方法。拟通过EOM(Electro-Optic Modulator)将测距伪随机码和通信码调制至主激光相位中,再传输至远端航天器。在远端航天器通过锁相环和延迟环组成的解调系统计算伪随机码的时间延迟,进而解析出卫星间的绝对距离和通信信息。相关结论可为未来的验证实验奠定理论和技术基础,同时为我国未来空间引力波探测的相关技术发展提供一定参考

Linearity performance analysis of the differential wavefront sensing for the Taiji programme

The Taiji programme is a Chinese space-based laser interferometer gravitational wave detection mission and the differential wavefront sensing (DWS) technique is introduced to reduce the effect of the laser pointing noise. As the distance between two adjacent satellites is about , the wavefront of the receiving beam is a flat top beam. In this paper, we construct an analytical model of the DWS signal under the circumstances of Gaussian beam-flat top beam interference and study the linearity performance. The position offset of the beams is found to greatly affect the linearity range. A numerical method is used to simulate the linearity range of the DWS signal under various operating conditions. The linearity range decrease with the increase of the offset angle of the Gaussian beam and the offset length of the flat top beam. The offset range of the beams based on the requirement of the Taiji is given at last

Study on the characteristic properties and genesis of land desertifi-cation in the agriculture and husbandry interlace zone

通过对陕北农牧交错带不同类型沙化土地土体构型、土壤质地、元素组成和理化性质的分析 ,研究了土地沙化的本质。结果表明 :受风沙作用影响 ,土壤中细粒物质逐渐减少 ,颗粒组成变粗 ;表层消失 ,最终被流沙所取代 ,原土壤剖面被覆盖在沙层之下 ;土壤有机质及养分含量减少 ,保水保肥性能降低 ,生产力不断下降 ;现代土壤形成过程以侵蚀和风沙沉积为主 ,物质淋溶和化学风化微弱。研究区土地沙化可划分为 :风沙侵蚀为主、风沙蚀积平衡、风沙沉积为主和土壤形成发育 4个阶段 ;沙化土地的类型有 :肥力衰退质地粗化、表层剥蚀、片沙覆盖、流动沙丘与固定沙丘等 5种

太极计划激光指向调控方案介绍

空间引力波探测中为实现引力波信号科学测量,卫星发射到预定轨道后需首先完成百万公里级激光链路的构建。同时为保证引力波信号不会被激光指向噪声淹没,激光指向稳定性需达到nrad/((Hz)~(1/2))量级。为此需设计一套复杂而精密的激光指向调控方案。本文以太极计划为背景,详细阐述了可采用的指向调控方案。拟将整个过程将分为两个阶段,首先进行激光捕获过程,在该过程中,使用星敏感器(STR)与电荷耦合器件(CCD)作为辅助捕获探测器,将激光指向不确定区域控制到μrad量级。之后进行激光精密指向过程,利用差分波前敏感测角(DWS)技术对激光指向稳定性进行控制。根据太极计划要求,对各阶段捕获探测器提出了视场及精度要求,并论述了采用DWS技术实现精密指向的可行性。相关结论可为未来的验证实验奠定理论基础,对太极计划指向系统构建提供参考

基于CPD模型的蔚州长焰煤热解特性研究

不同煤种成分的差异导致热解产物分布不同,CPD热解模型是精确预测煤热解产物分布规律的重要手段之一。采用非线性拟合方法对现有CPD模型进行修正,确定适用于蔚州长焰煤的5个化学结构参数,并通过热重实验对比分析了CPD修正模型的精确性

Soil Quality Evaluation Under Different Land Use in Southern Ningxia Mountain Area

运用层次分析法对研究区域的土壤进行了较为全面、较为科学的评价依据隶属函数确定了各评价指标的隶属度,实现了原始数据的归一化处理;同时也利用主成分分析法确立了各评价因子的权重分配问题。通过对研究区域土壤质量的评价,充分表明了土地利用方式不同对于土壤的改良效果存在明显差别灌木林地&gt;天然草地&gt;农地&gt;人工草地&gt;果园