主动光钟研究进展

自2005年至今，主动光钟经过了近20年的发展。主动光钟利用原子系综作为增益介质，其受激辐射可直接作为钟激光信号。因为主动光钟工作在坏腔区域，因此具有腔牵引抑制和窄线宽两个显著的优点，可以有效克服被动光钟存在的腔长热噪声问题。由于其优越的性能，主动光钟受到了国内外同行的广泛关注。根据实现方式不同，本文将主动光钟划分为原子束型主动光钟、基于激光冷却和光晶格囚禁的主动光钟、原子束及光晶格“复合型”主动光钟、法拉第主动光钟、离子阱囚禁型主动光钟以及热原子气室型主动光钟。对于不同类型的主动光钟，本文详细介绍了其实验及理论研究进展，并分析其优劣。最后，分析了主动光钟在精密测量领域的应用并展望了主动光钟的发展方向，为推动主动光钟的广泛应用提供借鉴。     

中国计量院成功研制出铯原子喷泉基准钟(NIM6)

本刊讯近日,中国计量院攻克了冷原子制备、冷却和探测、超稳微波产生、时标驾驭等关键技术,成功研制出铯原子喷泉基准钟(NIM6)、超稳微波源等。NIM6频率不确定度优于5.8E-16,相当于5400万年不差1秒;项目成果为北京卫星导航中心时间频率系统标准时标的产生、保持、改进和比对提供计量支撑,进一步确立中国计量院在时间频率研究领域的地位和作用。中国科学院武汉物理与数学研究所的两台可搬运钙离子光钟、上海光机所和华力创通的两台铷原子喷泉钟分别搬到中国计量院进行频率测量和比对。北京大学等多家单位的国产化小铯钟搬运到计量院进行比测。NIM6的成功研制,对建设我国独立自主、准确可靠的时间频率体系具有重要意义。     

枪弹初速激光测试系统方案设计

叙述了利用激光光幕测试枪弹初速的基本原理,并对激光光幕的形成、测试电路的实现、利用微机进行高精度测速、机械装置的实现等提出了一套可行的方案.在机械装置具有足够高精度的前提条件下,该测试系统能够实现高精度枪弹初速的测试.     

NIM的微波－光学频率基准研究 ———复现米和秒定义

报道中国计量科学研究院（NIM）在微波－光学频率计量研究的新进展：用NIM４激光冷却－铯原子 喷泉钟复现国际单位制（SI）时间单位秒（s）,用飞秒（FS）光学频率梳间接复现长度单位米（m）并标定稳频 激光波长实际实施米定义。NIM４铯原子喷泉钟的不确定度达到５×１０－１５,飞秒（FS）光梳锁定到NIM４钟控制的 氢钟后,其频率不确定度为２畅２×１０－１４。在此基础上讨论铯原子喷泉钟、稳频激光、FS光梳的作用、意义和相互 关系。最后简要介绍NIM５铯原子喷泉钟的研究进展和２００６年起NIM立题研制锶原子存储     

NIM的微波-光学频率基准研究——复现米和秒定义

报道中国计量科学研究院(NIM)在微波-光学频率计量研究的新进展:用NIM4激光冷却-铯原子喷泉钟复现国际单位制(SI)时间单位秒(s),用飞秒(FS)光学频率梳间接复现长度单位米(m)并标定稳频激光波长实际实施米定义.NIM4铯原子喷泉钟的不确定度达到5×10-15,飞秒(FS)光梳锁定到NIM4钟控制的氢钟后,其频率不确定度为2.2×10-14.在此基础上讨论铯原子喷泉钟、稳频激光、FS光梳的作用、意义和相互关系.最后简要介绍NIM5铯原子喷泉钟的研究进展和2006年起NIM立题研制锶原子存储光钟.     

钙离子光频标钟跃迁绝对频率测量

回顾了中国科学院精密测量科学与技术创新研究院对钙离子光频标钟跃迁绝对频率的测量工作，并对测量结果被国际计量委员会（CIPM）下属的时间频率咨询委员会（CCTF）采纳的情况进行了总结和描述。在2011～2020年间，利用实验室型光频标和可搬运光钟，采用基于飞秒光梳和卫星链路的方案溯源到国际秒定义，及基于飞秒光梳直接溯源到中国计量科学研究院铯喷泉微波钟的方案，多次测量了钙离子光频标钟跃迁绝对频率，测量不确定度从10^-15量级逐步提高到10^-16量级，共计4个测量结果被CCTF采纳。参与钙离子光频标钟跃迁频率国际推荐值的计算，分别于2012年、2015年、2017年和2021年先后四次更新了钙离子光频标钟跃迁频率推荐值。钙离子光频标钟跃迁于2021年被推荐为新增的“秒的次级表示”。     

从长度单位米到时间单位秒:稳频激光-飞秒光梳-铯原子喷泉钟-光钟

报道了中国计量科学研究院(NIM)在复现国际单位制(SI)长度单位米和时间单位秒的研究进展,包括稳频激光、NIM4铯原子喷泉钟和飞秒光学频率梳.NIM4钟不确定度达4.4×10-15,NIM在研的飞秒光梳将以优于1×10-13的不确定度实现光学波长向微波频率的溯源.文中还讨论了127I2饱和吸收633nm 3次谐波稳频的HeNe激光波长比5次谐波稳频的更"准确";指出飞秒光梳是从动跟踪系统,描述它的性能指标应当是它的跟踪精度;估计了用"吸收室-原子束-原子喷泉-原子/离子存储"4种不同原理所建频标可能达到的不确定度极限.最后简略展望时间频率基准研究的新动向--光钟.     

枪弹初速激光测试系统方案设计

叙述了利用激光光幕测试枪弹初速的基本原理，并对激光光幕的形成，睡的实现，利用微机进行高精度测速，机械装置的实现等提出了一套可行的方案。在机械装置具有足够高精度的前提条件下，该测试系统能够实现间初速的测试。     

激光回馈精密测量技术及应用

介绍了激光回馈干涉的理论模型,阐述了激光回馈测量灵敏度高、装置结构简单、可自准直、能够对非合作目标进行精密测量的技术特点。探讨了激光回馈测量技术在工业和科研领域中的应用方向,包括位移、角度、振动、绝对距离测量等,指出利用倍频复用、频率复用、偏振复用、全程准共路等技术可提高回馈测量的应用性能。分析了激光回馈测量相较传统干涉测量的优势,展望了激光回馈测量技术在科学研究、工业生产、精密制造等领域的应用前景,提出通过提高光源稳频精度、研究不同光回馈水平下的实验现象和理论模型、探索新型激光器的回馈效应等方式,进一步提升激光回馈干涉仪的灵敏度和测量性能。     

长距离高精度激光准直技术的最新发展

激光准直技术已广泛应用于大型工件直线度、同轴度、平面度等形位误差的测量.本论文主要介绍近年来激光准直技术的最新发展,如反馈控制法、无衍射光莫尔条纹法等.这些激光准直技术从理论到实践都较好地克服了激光漂移、大气环境对激光准直的影响,较好地满足了长距离高精度形位误差测量的要求.     

Die optische Atomuhr geht in die Anwendung

For The Most Accurate Time: The Optical Atomic Clock Enters Application The age of quantum technologies has begun. This is accompanied not only by the availability of additional physical quantities, which require a general rethink, but also by modified devices in which such states can be made possible. Within the opticlock project, an optical ion clock is being developed that exceeds today's standard of time measurement by more than a factor of ten in terms of stability and accuracy. An essential component of the opticlock is the compact vacuum chamber. The appropriate material, a design precisely tailored to the application, tight manufacturing tolerances and precision cleaning in accordance with defined Vacom standards allow the opticlock chamber to be transferred from a highly complex laboratory setup into a user‐friendly and transportable overall system. The targeted transfer of scientific research results to industry and their economic realization form the basis for developing a robust and durable optical ion clock, which can even be operated outside a specialized laboratory for the first time.     

Experimental demonstration of a compact and high-performance laser-pumped rubidium gas cell atomic frequency standard

The authors present a compact high-performance laser-pumped Rubidium atomic frequency standard exploiting the advantages of laser optical pumping for improved stability. The clock is based on an industrial Rb clock with the lamp assembly removed and optically pumped by light from a compact frequency-stabilized laser head. The modification of the buffer gas filling in the clock resonance cell reduces instabilities on medium-term timescales arising from the ac Stark effect and temperature variations. The frequency stability of the demonstrator clock was measured to be better than 4/spl times/10/sup -12//spl tau//sup -1/2/ up to 10/sup 4/ s, limited by the local oscillator (LO) quartz and RF loop electronics. Long-term drifts under atmosphere amount to 2-6/spl times/10/sup -13//day only, comparable to or lower than that for lamp-pumped clocks under similar conditions. Typical signal contrasts lie at around 20%, corresponding to a shot-noise limit for the short-term stability of 2/spl times/10/sup -13//spl tau//sup -1/2/. The results clearly demonstrate the feasibility of a laser-pumped Rb clock reaching <1/spl times/10/sup -12//spl tau//sup -1/2/ in a compact device (< 2 L, 2 kg, 20 W), given the optimization of the implemented techniques. Compact high-performance clocks of this kind are of high interest for space applications such as telecommunications, science missions, and future generations of satellite navigation systems [GPS, global orbiting navigation satellite system (GLONASS), European satellite navigation system (GALILEO)].     

GPS在轨卫星原子钟性能评估

卫星钟在轨性能评估对于卫星钟差预报与系统完好性监测具有重要作用。利用国际GNSS服务组织发布的事后GPS精密卫星钟差数据,基于频率准确度、漂移率、万秒稳定度及天稳定度对GPS Block IIR、IIR-M、IIF与IIIA 4类卫星的星载钟性能进行评估。结果表明:1) GPS卫星钟的频率准确度与天漂移率分别在10^-13～10^-12量级与10^-15～10^-14量级;2) 星载铷钟的万秒稳定度与天稳定度分别可达10^-14与10^-15量级,比星载铯钟的同类指标高近一个数量级;3) 新型Block IIIA卫星的星载钟的天稳定度比另外3种类型卫星的星载钟的天稳定度更高,达到(3～5)×10^-15的水平;4) 无论对于不同系列卫星还是同一系列卫星,各星载钟之间均存在一定的性能差异,这种差异与卫星钟在轨运行时间长短无显著关系。     

When should we change the definition of the second?

The microwave caesium (Cs) atomic clock has formed an enduring basis for the second in the International System of Units (SI) over the last few decades. The advent of laser cooling has underpinned the development of cold Cs fountain clocks, which now achieve frequency uncertainties of approximately 5×10(-16). Since 2000, optical atomic clock research has quickened considerably, and now challenges Cs fountain clock performance. This has been suitably shown by recent results for the aluminium Al(+) quantum logic clock, where a fractional frequency inaccuracy below 10(-17) has been reported. A number of optical clock systems now achieve or exceed the performance of the Cs fountain primary standards used to realize the SI second, raising the issues of whether, how and when to redefine it. Optical clocks comprise frequency-stabilized lasers probing very weak absorptions either in a single cold ion confined in an electromagnetic trap or in an ensemble of cold atoms trapped within an optical lattice. In both cases, different species are under consideration as possible redefinition candidates. In this paper, I consider options for redefinition, contrast the performance of various trapped ion and optical lattice systems, and point to potential limiting environmental factors, such as magnetic, electric and light fields, collisions and gravity, together with the challenge of making remote comparisons of optical frequencies between standards laboratories worldwide.     

A Dual Frequency VLF Timing System

The use of high precision portable clocks and radio signals is discussed in relation to synchronization of remotely located clocks. The demonstrated inherent phase stability, approximately ten ?s rms, of very-low-frequency (VLF) propagation and its low attenuation rate with distance, have led to various approaches to exploit these virtues in timing applications. The system considered here employs two carrier frequencies with timing information contained in their difference frequency to permit identification of a specific cycle of one of the carrier frequencies. Such a system makes stringent demands on phase stabilities of the transmitted signals and of the receiving system as well as that of the propagation medium itself. The present system, whose development has been supported jointly by NBS and NASA, makes use of NBS radio station WWVL at Fort Collins, Colo. Receivers are of the standard VLF phase tracking servo type. A special signal generator is used in conjunction with the local clock to simulate the transmitted signal in order to relate the local time scale to that at the transmitter. One of the carrier frequencies is maintained at 20 kHz. With a second frequency (500 Hz removed from this frequency), carrier cycle identification was achieved on about 90 percent of the days for over a month on the path from Fort Collins, Colo., to Greenbelt, Md. Since January 4, 1966, the difference frequency has been 100 Hz, with somewhat more fluctuation in results. However, lower precision is required for the initial synchronization.     

Observation and cancellation of a perturbing dc stark shift in strontium optical lattice clocks

We report on the observation of a dc Stark frequency shift at the 10-(13) level by comparing two strontium optical lattice clocks. This frequency shift arises from the presence of electric charges trapped on dielectric surfaces placed under vacuum close to the atomic sample. We show that these charges can be eliminated by shining UV light on the dielectric surfaces, and characterize the residual dc Stark frequency shift on the clock transition at the 10-(18) level by applying an external electric field. This study shows that the dc Stark shift can play an important role in the accuracy budget of lattice clocks, and should be duly taken into account.     

Clock stability characterization and measurement intelecommunications

Clock stability characterization and measurement for telecommunications pose peculiar issues and requirements. This paper aims to provide an overview on this subject. After briefly recalling the background work, the key features and issues of clock stability characterization and measurement in telecommunications are described. The timing signal reference model and the stability quantities adopted in the new international standards are introduced and the impact of the measurement configuration and of the time error sampling period on their behavior are elucidated. The measurement of clock stability in telecommunications is then addressed, and a standard practical measurement procedure is outlined. Several measurement results are provided to support the concepts expounded with experimental evidence. The results shown have been chosen among those obtained throughout the last three years by testing clerks of digital switching exchanges, clocks for synchronous digital hierarchy (SDH) equipment, and state-of-the-art stand-alone slave clocks for synchronization networks. They thus represent a survey of the actual performance of clocks currently deployed in telecommunications networks     

阿秒时间抖动的全保偏掺铒光纤激光器

近年来，超稳光生微波和远距离时频同步等高精度、高速科学研究对低噪声飞秒光纤激光器具有迫切的需求。为实现低时间抖动噪声的激光种子源，基于“光积木”结构，设计并搭建了一台重复频率为100 MHz的全保偏掺铒锁模光纤激光器，“光积木”结构可以有效地抑制激光器的机械噪声和重频漂移。采用平衡光学互相关技术，首次从全保偏锁模光纤激光器的出射脉冲中直接进行了高精度的时间抖动测量。该激光器在傅里叶频率10 kHz至1 MHz的积分区间内，积分均方根时间抖动仅为98.36 as。     

Research on real time detection of departure angle for the laser beam through atmospheric channels

The precision of departure angle detection for the laser beam can be improved by optimizing algorithms by which the high precision and stability of the laser beam pointing and tracking would be obtained, namely, improving the performance and accommodation of the free space optical communications. Atmospheric turbulence-induced optical intensity scintillations have a strong impact on the location precision of the laser spot through the atmospheric channels. Consequently, new requests come into view for the optimization of the algorithms. In the paper, the advantages and disadvantages of the traditional centroid method are analyzed. In terms of variations of laser spot, combined with the requests for real-time detection of departure angle, we proposed a new detection method. The edge of the laser spot on the detection sensor was redefined, and then the redefined spot was used to calculate the departure angle of the laser beam. The results of the simulations and experiments show that the precision of departure angle detection has been improved by more than 16%, which could reduce the effect of detection errors on the tracking procedure.