共查询到20条相似文献,搜索用时 156 毫秒
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频率是电磁波最重要的一个基本物理量,随着THz技术的发展,在光源研制、宽带通信、超精细光谱测量等领域都对THz频率的高精度侧量提出了要求.传统的Fabry-Perot干涉法与外差探测法难以实现THz频率的高精度测量,频率梳方法虽然测量精度很高,但测量系统复杂.本文提出一种利用重复频率自由漂移的飞秒激光器实现太赫兹频率精密测量的新方法.通过对非锁定的飞秒激光器的重复频率和THz拍频频率进行同时连续采集与计算,得到被测THz频率,测量精度可以达到10~(-10)量级无需对飞秒激光重复频率进行复杂的锁定控制,测量系统大大简化. 相似文献
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Rydberg原子具有极大的极化率和微波跃迁偶极矩,对外界电磁场非常敏感,可实现基于Rydberg原子的超宽频带射频电场的高分辨高灵敏测量.通过Rydberg原子的全光学无损的电磁感应透明探测手段,可以实现基于原子的快速免校准宽频带(0.01-1000 GHz)外电场的精密测量.对于频率大于1 GHz的微波场,由微波场耦合相邻Rydberg能级形成的Autler-Townes分裂进行测量;而对于频率小于1 GHz的长波射频场,由Rydberg能级的射频边带能级进行测量.这种方法是基于原子能级参数,可溯源到基本物理常量,不依赖于外界参考;且对电场无干扰,易于实现微型化和集成化,具有广泛的应用前景.本文主要综述了基于Rydberg原子的外电场测量的最新研究进展,重点介绍长波长射频场的测量,包括电场强度、频率以及极化方向的测量,详细介绍了其测量原理和探测灵敏度,并讨论了其应用前景及未来发展方向. 相似文献
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为了满足冷原子干涉实验对时序控制的需求,设计并实现了一个基于LABVIEW软件的激光时序控制DDS系统,其工作过程为通过设计的LABVIEW上位机软件输入需要产生的频率和频率间隔时间,ARM芯片根据LABVIEW软件发送来的控制信息实现对射频信号芯片的控制,CPLD芯片用来控制射频信号之间的时间间隔,最后DDS芯片产生与控制信息相对应的射频信号。与目前同类装置相比,系统实现了跳频时间和频率更加精确和工作稳定性更好。经过系统的调试分析以及性能测试,DDS跳频系统能够满足原子干涉仪激光时序控制需求。通过测试DDS装置,DDS装置能够输出准确输出射频频率值,并且射频频率时间间隔能精确到微秒。DDS装置可以有效控制冷原子干涉仪的激光时序,在探询时间为120毫秒且重复率为2.2赫兹的情况下,冷原子重力仪的重力测量灵敏度达到 。 相似文献
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近年来,冷原子技术和激光技术促进了高精度光频标的发展,有望在建立时间基准、推动基础研究和满足国家需求等方面发挥重要的作用.本文介绍了中国科学院武汉物理与数学研究所近年来在高准确度钙离子(~(40)Ca~+)光频标研究方面的进展:采用新的ULE腔系统,实现了729 nm钟跃迁激光器1—100 s的频率稳定度均优于2×10~(-15),通过对外场和环境效应的控制及克服,特别是囚禁离子运动效应的抑制,获得单个钙离子光频标的不确定度优于5.5×10~(-17);通过两台光频标的比对,测得20000 s的稳定度也进入10~(-17)量级;基于高精度钙离子光频标平台,进行了相关精密测量的工作,包括:基于全球定位系统的超高精度远程光频绝对值测量方案,第二次测量了钙离子的光频跃迁绝对值,该测量结果再次被国际时间频率咨询委员会采纳,更新了钙离子的频率推荐值;精确测量了钙离子的钟跃迁魔幻波长,由此提出新型的全光囚禁离子光频标的方法;精密测量了钙离子的亚稳态寿命等参数.以上工作推动了基于冷原子的精密测量工作. 相似文献
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San-Dan Wang Jin-Peng Yuan Li-Rong Wang Lian-Tuan Xiao Suo-Tang Jia 《Frontiers of Physics》2021,16(1):12502
We experimentally demonstrate the cesium electric quadrupole transition from the 6S1/2 ground state to the 7D3/2,5/2 excited state through a virtual level by using a single laser at 767 nm. The excited state energy level population is characterized by varying the laser power, the temperature of the vapor, and the polarization combinations of the laser beams. The optimized experimental parameters are obtained for a high resolution transition interval identification. The magnetic dipole coupling constant A and electric quadrupole coupling constant B for the 7D3/2,5/2 states are precisely determined by using the hyperfine levels intervals. The results, A = 7.39 (0.06) MHz, B = −0.19 (0.18) MHz for the 7D3/2 state, and A = −1.79 (0.05) MHz, B =1.05 (0.29) MHz for the 7D5/2 state, are in good agreement with the previous reported results. This work is beneficial for the determination of atomic structure information and parity non-conservation, which paves the way for the field of precision measurements and atomic physics. 相似文献
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在室温下的原子气室中, 基于铯原子6S1/2-6P3/2-7S1/2(852.3 nm+1469.9 nm) 阶梯型能级系统, 利用电光调制器的主频和±1级边带分别产生的三套双共振吸收光谱, 当驱动电光调制器的信号源频率严格等于7S1/2态超精细分裂的能级间隔时, 三套谱线中的一些超精细跃迁谱线重叠且线宽最窄, 利用这一现象很好地避免了激光器频率扫描时非线性效应的影响, 测量出了7S1/2 态超精细分裂能级间隔: 2183.72 MHz±0.23 MHz, 并计算出该态的磁偶极超精细常数: Ahfs= 545.93 m MHz±0.06 MHz, 与文献中报道的测量结果一致. 相似文献
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测量了15~300K温度范围内57.5%Al1.5O-35%CaO-7.5%BaO玻璃中四价铬的发射光谱.这种材料中铬离子的能级处于Tanabe-Sugano图上弱场范围中,最低的激发态是3T2,发射谱是一个宽带.按照单频近似理论拟合低温下的光谱,得到3T2能级的零声子线位置Ezp=8400cm-1,声子能量tω=320cm-1,黄昆因子S=358.尽管单频近似能够较好地描述低温下的线形,发射光谱宽度随温度的变化却与单频近似理论的结果不符.讨论了这种差别的原因,认为可能的解释是与激发态耦合的声子能量大于与基态耦合的声子能量. 相似文献
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基于~(85)Rb原子5S1/2-5P3/2-5D_(5/2)阶梯型能级系统(780 nm+776 nm),利用高信噪比的电磁诱导透明谱对~(85)Rb原子5D_(5/2)态超精细分裂进行测量.其中,频率校准是通过位相型电光调制器和共焦法布里-珀罗腔共同实现的.通过测量~(85)Rb原子5D′5/2态(F′=5),(F′′=4)及(F′′=3)之间的超精细分裂,我们确定了~(85)Rb原子5D_(5/2)态的磁偶极超精细相互作用常数(A=-(2.222±0.019)MHz)和电四极超精细相互作用常数(B=(2.664±0.130)MHz). 相似文献
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The diffusion of W on a (211) plane of a W field emitter has been re-examined by means of the fluctuation autocorrelation method. Diffusion along channels yielded E = 16.8 ± 0.5 kcal, D0 = (3 ± 1) × 10−5 cm2 s−1. For diffusion across channels E =6.6 kcal, D0 = 4 × 10−9cm2 s−1 at T < 752 K, and E = 24 kcal, D0 = 5 × 10−4 cm2 s−1 at T > 752 K. The results for diffusion along channels yield E and D0 values intermediate between recent results by Wang and Ehrlich [Surf. Sci. 206 (1988) 451] using field ion microscopy (E = 19 kcal, D0 = 7.7 × 10−3 cm2 s−1) and Tringides and Gomer [J. Chem. Phys. 84 (1986) 4049], using the same method as the present work but a larger slit (E = 13.3 kcal, D0 = 7 × 10−7 cm2 s−1). The results for cross channel diffus good agreement with those of Tringides and Gomer below 752 K, where these authors stopped. The new high temperature results suggest that the channel wall exchange mechanism postulated by Tringides and Gomer for cross channel diffusion at low T gives way to diffusion by climbing over the channel walls with higher E but also higher D0 above 752 K. Possible reasons for the discrepancies between these three sets of results and the absence of cross channel diffusion in the work of Wang and Ehrlich are briefly discussed. 相似文献
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A 35Cl nuclear quadrupole resonance (35Cl-NQR) investigation of polycrystalline Ca(ClO3)2·2H2O is described. The 35Cl-NQR frequencies (νQ) for two resonance lines (νQ1 and νQ2), the spin lattice relaxation time (T1Q) for νQ2 only and the line width δνQ2 were measured in the temperature range 292–345 K, except for the frequency measured up to 455 K. The observed decrease in the resonance frequencies with increasing temperature permitted the determination of the frequencies of librations of the ClO3− ion about two axes perpendicular to the three-fold axis of the ion mainly responsible for this effect. The temperature dependence of the relaxation time T1Q proved the occurrence of water diffusion and hindered rotation of ClO3− ions. The activation energies of these two molecular motions were determined, and their effect on the electric field gradient at the site of a chlorine nucleus was discussed. Temperature measurements of the line width δνQ2 confirmed the conclusions drawn from the analysis of T1Q(T). 相似文献
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里德伯态光谱是测量里德伯态能级结构和中性原子间相互作用的常用技术手段,特别是高精度的里德伯光谱,可以测量室温原子气室中由偶极相互作用等导致的原子能级频移.在实验中利用反向的852 nm激光和509 nm激光实现了室温原子气室中铯原子6S_(1/2)—6P_(3/2)—57S(D)跃迁的级联双光子激发,实现了里德伯态原子的制备.基于阶梯型电磁诱导透明获得了铯原子里德伯态的高分辨光谱.实验中,基于速度选择的射频边带调制技术,对光谱信号进行了频率标定,测量了铯原子里德伯态57D_(3/2)和57D_(5/2)的精细分裂,分裂间隔为(354.7±2.5)MHz,与理论计算结果基本一致.速度选择的射频调制光谱可以实现里德伯态原子的能级分裂测量,其测量精度对于单光子跃迁的绝对激光频率不敏感;实验中影响57D_(3/2)和57D_(5/2)精细分裂间隔测量精度的主要因素是功率加宽导致的电磁感应透明信号的展宽和509 nm激光频率扫描的非线性. 相似文献
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Dynamic behaviors of water contained in calcium-silicate-hydrate gel at different temperatures studied by quasi-elastic neutron scattering spectroscopy 下载免费PDF全文
The dynamic behaviors of water contained in calcium-silicate-hydrate(C-S-H) gel with different water content values from 10%to 30%(by weight),are studied by using an empirical diffusion model(EDM) to analyze the experimental data of quasi-elastic neutron scattering(QENS) spectra at measured temperatures ranging from 230 K to 280 K.In the study,the experimental QENS spectra with the whole Q-range are considered.Several important parameters including the bound/immobile water elastic coefficient A,the bound water index BWI,the Lorentzian with a half-width at half-maximum(HWHM) Γ_1(Q) and Γ_2(Q),the self-diffusion coefficients D_(t1) and D_(t2) of water molecules,the average residence times τ_(01)and τ_(02),and the proton mean squared displacement(MSD)(u~2) are obtained.The results show that the QENS spectra can be fitted very well not only for small Q(≤1 A~1) but also for large Q.The bound/immobile water fraction in a C-S-H gel sample can be shown by the fitted BWI.The distinction between bound/immobile and mobile water,which includes confined water and ultra-confined water,can be seen by the fitted MSD.All the MSD tend to be the smallest value below 0.25 A~2(the MSD of bound/immobile water) as the Q increases to 1.9 A~1 no matter what the temperature and water content are.Furthermore,by the abrupt changes of the fitted values of D_(t1),τ_(01),and Γ_1(Q),a crossover temperature at 250 K,namely the liquid-to-crystal-like transition temperature,can be identified for confined water in large gel pores(LGPs) and/or small gel pores(SGPs) contained in the C-S-H gel sample with 30% water content. 相似文献
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A. Birkan Seluk N. Tuluolu S. Karadeniz S. Bilge Ocak 《Physica B: Condensed Matter》2007,400(1-2):149-154
In this work, the investigation of the interface state density and series resistance from capacitance–voltage (C–V) and conductance–voltage (G/ω−V) characteristics in In/SiO2/p-Si metal–insulator–semiconductor (MIS) structures with thin interfacial insulator layer have been reported. The thickness of SiO2 film obtained from the measurement of the oxide capacitance corrected for series resistance in the strong accumulation region is 220 Å. The forward and reverse bias C–V and G/ω−V characteristics of MIS structures have been studied at the frequency range 30 kHz–1 MHz at room temperature. The frequency dispersion in capacitance and conductance can be interpreted in terms of the series resistance (Rs) and interface state density (Dit) values. Both the series resistance Rs and density of interface states Dit are strongly frequency-dependent and decrease with increasing frequency. The distribution profile of Rs–V gives a peak at low frequencies in the depletion region and disappears with increasing frequency. Experimental results show that the interfacial polarization contributes to the improvement of the dielectric properties of In/SiO2/p-Si MIS structures. The interface state density value of In/SiO2/p-Si MIS diode calculated at strong accumulation region is 1.11×1012 eV−1 cm−2 at 1 MHz. It is found that the calculated value of Dit (≈1012 eV−1 cm−2) is not high enough to pin the Fermi level of the Si substrate disrupting the device operation. 相似文献
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We report an experimental investigation on the Doppler-free saturated absorption spectroscopy of buffer-gas-cooled Barium monofluoride (BaF) molecules in a 4 K cryogenic cell. The obtained spectra with a resolution of 19 MHz, much smaller than previously observed in absorption spectroscopy, clearly resolve the hyperfine transitions. Moreover, we use these high-resolution spectra to fit the hyperfine splittings of excited A(v = 0) state and find the hyperfine splitting of the laser-cooling-relevant A2Π1/2(v = 0, J = 1/2,+) state is about 18 MHz, much higher than the previous theoretically predicted value. This provides important missing information for laser cooling of BaF molecules. 相似文献