２０００年ＮＩＭ铯冷原子喷泉时间频率基准装置研究的进展

本文报导了中国计量科学研究院（ＮＩＭ）研制新一代“激光冷却铯原子喷泉”国家时间频率基准装置的进展,实现了从磁光阱（ＭＯＴ）过渡到光学黏胶（ＯＭ）装载－冷却铯（Ｃs)原子,利用飞行时间（ＴＯＦ）法记录到信噪比优于４０的原子云荧光信号,原子经后冷却达到（１０－２０)uK,用光学黏胶从铯蒸气直接获得了冷原子云,并给出了对实验的讨论。     

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”。     

Primary Atomic Frequency Standards at NIST

The development of atomic frequency standards at NIST is discussed and three of the key frequency-standard technologies of the current era are described. For each of these technologies, the most recent NIST implementation of the particular type of standard is described in greater detail. The best relative standard uncertainty achieved to date for a NIST frequency standard is 1.5×10⁻¹⁵. The uncertainties of the most recent NIST standards are displayed relative to the uncertainties of atomic frequency standards of several other countries.     

Compression and localization of an atomic cloud in a time dependent optical lattice

We analyze a method of compressing a cloud of cold atoms by dynamic control of a far off-resonance optical lattice. We show that by reducing the lattice spacing either continuously or in discrete steps while cooling the atoms with optical molasses large compression factors can be achieved. Particle motion in the time-dependent lattice is studied numerically using a three-dimensional semiclassical model. Two experimentally realistic models are analyzed. In the first we continuously vary the lattice beam angles to compress atoms initially in a Gaussian distributed cloud with standard deviation of 250 µm into a single site of a two-dimensional lattice of area A ～ 35 × 35λ², with λ the wavelength of the lattice beams. This results in an optical depth for an on-resonant probe beam >80 which is an increase by a factor of about 1800 compared to the uncompressed cloud. In the second approach we use a discrete set of lattice beam angles to decrease the spatial scale of the cloud by a factor of 500, and localize a few atoms to a single lattice site with an area A ? λ².     

铯束原子频率标准装置测量不确定度的分析

时间计量已经广泛地用于现代科学技术的各个方面,并且用于对其它物理量的间接测量之中,因而作为时间频率量值传递系统中的一级频标——铯束原子频率标准不确定度分析就显的尤为重要。本文介绍了用铯束原子频率标准装置测量不确定度的评定过程,并给出了计算过程及表达方式。     

汞离子微波频标光学设计

汞离子微波频标利用汞灯进行抽运,可实现小型化,同时具备体积小、指标高的优势,未来可在卫星导航、深空探测和守时中得到广泛应用。为了提高抽运效率及降低噪底,需要进行汞灯光学设计,使抽运光通过四极阱中心与囚禁离子充分作用的同时减少与真空腔及四极杆的反射。首先提出遮挡光源法和非等比例放大法两种光学设计方法。然后介绍了两种设计方法的具体设计过程和设计结果,并比较了两种光学设计方法汞灯的能量利用率。最后利用非等比例放大法进行光路优化设计,并完成了物理系统信号探测实验。实验结果表明：采用该光学设计方案,汞离子光微波双共振跃迁信号幅度提高了20%以上。     

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.     

实现74 cm铯冷原子喷泉的实验和讨论

中国计量科学研究院NIM4 #激光冷却 铯原子喷泉钟实现了原子云 74cm喷泉 ,得到S N约 2 0 0的荧光飞行时间信号。文中介绍了对NIM4 #钟与上抛 回落 信号探测相关的改进 ,列举了喷泉参数 ,报导了喷泉实验和初步讨论     

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     

基于囚禁离子的微波频标研究进展

微波频标在卫星导航、精密计量、电力、通信等众多领域得到广泛应用,发挥了不可或缺的重要作用。近些年,国际上多家科研单位都在开展新型微波频标的研究,其中基于囚禁离子的微波频标具有高性能和小型化等优势,成为倍受关注的新一代微波频标。本文综述了离子阱微波频标的国内外研究现状,介绍了Penning阱和Paul阱两种常见离子阱的工作原理,以及¹⁹⁹Hg⁺,¹¹³Cd⁺,¹⁷¹Yb⁺等离子微波频标的研究动机、应用领域、技术方案和实现的技术指标。最后,本文对离子阱微波钟在守时钟、星载钟等方面的应用前景进行了展望。     

全固态飞秒光学频率梳研究进展及展望

自1999年至今,光学频率梳（Optical Frequency Comb,OFC）经历了二十多年的快速发展。基于飞秒激光的光学频率梳在频率计量学、超快光谱学、光学频率标准、阿秒脉冲的产生、多脉冲时域合成等众多前沿研究领域中发挥了不可替代的作用。特别是继飞秒钛宝石激光频率梳、飞秒光纤激光频率梳之后,基于二极管激光直接泵浦的全固态飞秒激光频率梳由于兼具钛宝石激光噪声低、重复频率高,光纤激光结构紧凑、电光效率高的共同优势,引起了许多研究组的兴趣,并取得系列有意义的进展。本文综述了全固态光学频率梳的发展和已取得的典型应用,并结合笔者所在课题组取得的研究成果,对全固态光学频率梳未来的发展方向进行展望,为促进全固态飞秒锁模振荡器的发展提供借鉴。     

1.5μm光纤通信波段乙炔稳频激光技术研究进展

1.5μm乙炔饱和吸收谱线是国际计量委员会(CIPM)正式推荐的光纤通信波段复现‘米’定义的频率参考标准。乙炔稳频激光依据稳频方法可分为线性吸收和饱和吸收两大类,饱和吸收相比线性吸收,能够消除乙炔分子的多普勒效应,获得线宽更窄、频率稳定度和复现性更高的稳频激光,1s频率稳定度能够达到10^-13量级,波长漂移为10^-12量级。利用13C2H2(ν1+ν3)P(16)谱线,研发的微型气室有望实现稳频激光的全光纤链路传播,为高度集成化、抗干扰能力强的稳频激光源提供了新的发展方向。高性能的1.5μm近红外稳频激光直接为密集波分复用系统、精密光纤传感等多个领域提供波长参考源,结合飞秒激光频率梳技术可进一步完善光纤通信中激光波长量值传递溯源体系,提升激近红外波段光波长的测量能力,为光纤波段的精密测量提供量值保障。     

Generation of Supercontinuum and Spectrum Broadening in Holey Fibers Subjected to Radiation from Continuous Femtosecond Visible and Infrared Lasers

Supercontinuum generation in holey fibers manufactured at the University of Bath (Great Britain) and at the Institute of Radioengineering and Electronics of the Russian Academy of Sciences is produced through use of a Ti:sapphire femtosecond laser. Broadening of the radiation spectrum of a Cr:forsterite femtosecond laser ( = 1250 nm) is observed in these fiber samples. The present study is part of a program intended for the creation of an optical femtosecond synthesizer stabilized relative to a methane optical frequency standard ( = 3390 nm).     

A Search for Optical Molasses in a Vapor Cell: General Analysis and Experimental Attempt

We analyze the application of optical molasses to a thermal vapor cell to make and collect cold atoms. Such an arrangement would simplify the production of cold atoms by eliminating the difficulty of first having to produce and slow an atomic beam. We present the results of our calculations, computer models, and experimental work. As a guide for future work, general results are given to illustrate which fundamental parameters are most important in the production of cold atoms in a vapor cell.     

飞秒激光频率梳测量光频用拍频装置的实验研究

飞秒激光频率梳测量光频实验中会遇到拍频信号信噪比低、高信噪比拍频信号维持时间短的问题。本文针对该问题在光路的准直、稳定维持方面采取了相应的光学、机械结构优化以及对拍频信号采取了先滤波后放大的措施;设计了一种拍频装置,并利用该装置进行了碘稳频633 nm激光器e峰频率的绝对测量实验。     

法拉第滤光器在法拉第激光器领域研究进展

法拉第激光器是一种利用法拉第反常色散原子滤光器作为选频元件的新型外腔半导体激光器,原理上法拉第激光的输出波长随着激光二极管驱动电流及工作温度的变化,始终与原子跃迁谱线相对应,可以将激光频率有效地锁定至原子跃迁谱线,实现窄线宽的激光输出信号,并且短期与长期频率稳定性均较好。本文详细介绍了自1845年法拉第旋光效应提出以来,法拉第反常色散原子滤光器的发展历程,法拉第激光器的工作机理、发展历程以及性能优越性,并结合国内外的研究进展,介绍了法拉第激光发展各个阶段的技术瓶颈及相应的解决办法,同时展望了法拉第激光器未来在量子领域特别是量子精密测量领域的重要价值。     

Investigation of the error in transferring the dimensions of the volt using a transportable stabilitron voltage standard

The results of an investigation of the characteristics of transportable voltage standards based on stabilitrons for the purpose of using them as standards of comparison when transferring the dimension of the unit of constant voltage in accordance with the State Standard GOST 8.027-2001 are presented. It is shown that, using the standard investigated, one can transfer the dimensions of the unit of voltage with an overall relative error of 5·10⁻⁸ for a voltage of both 1.018 V and 10 V. __________ Translated from Izmeritel'naya Tekhnika, No. 1, pp. 34–38, January, 2006.     

Modeling of difference frequency radiation energy redistribution process in a spectrum of laser pulse of a few optical cycles propagating in a quasi-phase-matching GaAs crystal

We present the results of a numerical study of the generation process of difference frequency radiation (DFR) arising via the interaction of mutually orthogonal linearly- polarized few-cycle laser pulses propagating in a quasi-phase-matching (QPM) GaAs crystal. Considered the interaction of pulses having the central wavelengths of 1.98 µm, duration of 30 fs with the electric field amplitude 200 MV/m, propagating along the normal to the ?110? plane. The period Λ of the QPM GaAs crystal in numerical simulations varied from 20.89 µm to 53.23 µm. It is shown that by changing the grating period of the QPM GaAs crystal from 23.02 µm to 37.29 µm it is possible to improve the efficiency of QPM generation of DFR in the 5.48 µm – 10.12 µm spectral range at least by 8 dB in comparison with the generation of DFR in bulk crystal GaAs in the same spectral range.     

Impact of second-order PMD in a coherent optical orthogonal frequency division multiplexing system

The second-order, polarization-mode dispersion (PMD) effect for coherent optical orthogonal frequency division multiplexing (CO-OFDM) system in long-haul transmission with single-mode fiber was analyzed in detail. The closed-form expression is presented for the time impulse response of an OFDM signal affected by second-order PMD. Analysis and simulation results show that, compared with polarization-dependent chromatic dispersion (PCD), CO-OFDM system performance is mainly influenced by depolarization rate (DR) which can moderate phase noise induced by chromatic dispersion. For a fiber link of 800 km and DR of 30 ps, the system Q value is improved by about 1.3 dB over the case of no DR.