200 km沙漠链路高精度光纤时频传递关键技术研究

针对沙漠环境实地链路存在的温度变化大、室外风力、地表振动等多种复杂噪声来源,通过对系统反馈补偿带宽、反馈补偿强度、光功率等时频传递系统关键参数的优化配置,研究了不同反馈补偿参数下复杂链路噪声的有效抑制技术.全链路的频率传递稳定度8×10~(-14)@1s,1×10~(-16)@1000 s,千秒尺度下时间信号传递的时间方差仅为1.2 ps.实现了氢钟信号在200 km量级沙漠环境实地链路的无损传输.该验证实验在基于短基线干涉测量的卫星测轨系统中发挥了重要作用.     

Fiber-based multiple-access frequency synchronization via 1f–2f dissemination

Considering the reference frequency dissemination requirements of the Square Kilometre Array telescope(SKA)project,on the basis of the 1f–2f precision frequency synchronization scheme,we propose and demonstrate a fiber-based multiple-access frequency synchronization scheme.The dissemination reference frequency can be recovered at arbitrary nodes along the entire fiber link.It can be applied to antennas close proximity to the SKA central station,and will lead to a better SKA frequency synchronization network.As a performance test,we recover the disseminated 100-MHz reference frequency at an arbitrary node chosen as being 5 km away from the transmitting site.Relative frequency stabilities of2.0×10~(-14)/s and 1.6×10~(-16)/10~4 s are obtained.We also experimentally verify the feasibility of a frequency dissemination link with three access points.     

基于光纤的光学频率传递研究

随着光钟研究的发展, 光钟的稳定度和不确定度均达到10^-18量级. 通过光纤可以实现光钟频率信号的高精度传输, 有望用于未来“秒”定义的复现. 演示了百公里级实验室光纤上的光学频率传递. 对于在实验室70 km光纤盘上实现的光频传递, 光纤相位噪声抑制在1-250 Hz傅里叶频率范围内均接近于光纤延时极限, 对应传输稳定度(Allan偏差)为秒级稳定度1.2×10^-15, 10000 s稳定度为1.4×10^-18. 实验室100 km光纤的光频传递秒级稳定度也达到了5×10^-15. 提出了光纤噪声用户端补偿的方案, 可以简化星形传递网络中心站的复杂度. 在25 km光纤上演示了该传递方案, 实现的传输稳定度接近传统前置补偿传递方案.     

用于光频传递的通信波段窄线宽激光器研制及应用

通信波段窄线宽激光器在基于光纤的光学频率传递中有着重要应用. 本文报道了1550 nm超窄线宽光纤激光器的研制及其在光学频率传递中的初步应用结果. 利用一台激光光源, 分别锁定到两个参考腔上(精细度分别为344000和296000), 锁定后经拍频比对测得单台激光线宽优于1.9 Hz, 秒级频率稳定度为1.7×10^-14, 优于国内同类报道. 将研制的超窄线宽激光器用于光纤光学频率传递, 在50 km光纤盘上实现了 7.5×10^-17/s的传递稳定度, 较采用商用光纤激光器提高了3.2倍.     

The Two-Nucleon Mechanism for the Neutrinoless Double Beta Decay and the BCS Nuclear Wave Function

A method of using the Bardeen-Cooper-Schrieffer (BCS) nuclear wave function to treat the two-nucleon mechanism for neutiinoless double beta decay process 0⁺ → 0⁺ is proposed.The neutrinoless decay mode and the neutrinoless decay accompanied by a Majoron emission mode of ⁸²Se are studikd. Our cdculated results show that to reproduce the experimental value of γ^(ov) > 1.8 × 10²² yr for neutrinoless double beta decai of ⁸²Se the Majorana neutrino mass m_v < 6.2 eV and the mixing parameter of right-handed current η < 7.0 × 10^-6 In the emission with a Majoron mode the effective Majoron coupling to neutrino is deduced from the experimental value of γ^(ov,H) > 4.4 × 10²⁰ yr for ⁸²Se with the result H0> < 6.2 × 10^-4.     

AlN插入层对AlxGa1-xN/GaN界面电子散射的影响

本文研究AlN作为Al_xGa_1-xN/GaN插入层引起的电子输运性质的变化, 考虑了Al_xGa_1-xN和AlN势垒层的自发极化、压电极化对Al_xGa_1-xN/AlN/GaN双异质结高电子迁移率晶体管(HEMT)中极化电荷面密度、二维电子气(2DEG) 浓度的影响, 分析了AlN厚度与界面粗糙度散射和合金无序散射的关系; 结果表明, 2DEG 浓度、界面粗糙度散射和合金无序散射依赖于AlN层厚度, 插入一层1–3 nm薄的AlN层, 可以明显提高电子迁移率.     

A cold thermionically emitting dusty air plasma formed by radiativeheating of graphite particulates

Formation of an atmospheric pressure dusty air plasma is explored experimentally in this paper. The plasma is created by seeding an air flow with graphite particles and irradiating the particulates with a focused CO₂ laser beam. The graphite particles are, thus, heated to thermionically emitting temperatures, and average particle temperatures and average particle number densities are measured. The presence of charges is inferred both from these measured quantities using a simple theoretical transient model, and experimentally by applying a dc bias across the irradiated region. It is found that an electron density of ~6.7 × 10⁵ cm^-3 (6.7 × 10¹¹ m^-3) can be produced at steady state in the presence of O₂. This value can be increased to 3.6 × 10⁷ cm^-3 (3.6 × 10¹³ m ^-1) in the ideal case where an electron attachment to O₂ is suppressed and where a lower work function particulate is used     

Pressure dependence of plasma parameters in medium-vacuum nitrogenarc discharge with the titanium cathode

The plasma properties of a medium-vacuum nitrogen arc discharge from a titanium cathode were studied. The arc chamber use was 400 mm in diameter and 600 mm in length. The cathode diameter and thickness were 64 and 25 mm, respectively. The experimental conditions are given as follows: pressure range=1×10^-3~2×10^-1 torr; N₂ gas flow rate=6 ml/min; arc current=50 A. Electric probe characteristics are measured as a function of pressure and distance from the cathode surface. The analytical results obtained show that the electron energy distribution takes 1-Mx at pressures above 1×10^-2 torr but 2-Mx at pressures under 4×10^-2 torr and that the electron density has a maximum value at a certain pressure. The Ti⁺, Ti⁺⁺, and N ⁺₂ ion spectral intensities are measured as a function of pressure and distance from the cathode surface. On comparison of these results and the electron density, the Ti⁺ spectral intensity turns out to be proportional to that of the electron density. This suggests that the major ion in the plasma volume is of the Ti⁺ species     

Effects of a Family Non-universal Z' Boson in \bar{B}_d→μ+μ- and B- →π-μ+μ-,ρ-μ+μ- Decays

Motivated by the recently updated experimental measurement on \bar{B}_d→μ⁺μ^- and B^-→π^-μ⁺μ^- decays by CDF and Belle collaborations, we revisit these
decays, as well as B^-→ρ^-μ⁺μ^- decay, within the Standard Model, and evaluate the effects of a family non-universal Z' boson. Under the constraint from {\cal B}(B^-→π^-μ⁺μ^-), we find the ranges of the Z' couplings S^LR_μμ< -5.2×10^-2 or D^LR_μμ < -8.1× 10^-2 are excluded. Within the allowed Z' parameters spaces, comparing with the SM predictions, we find that {\cal B}(\bar{B}_d→ μ⁺μ^-, {\cal B}(B^-→ π^-μ⁺μ^-), and {\cal B}(B^-→ρ^-μ⁺μ^-) could be enhanced by a factor about
226%, 245%, and 254%, respectively, byZ' contributions. However, they are hardly to be reduced. Furthermore, the zero crossing in the normalized forward-backward asymmetry spectrum of B^- →ρ^-μ⁺μ^- decay at low dimuon mass always exists.     

Negative thermal expansion and photoluminescence in solid solution(HfSc)_(0.83)W_(2.25)P_(0.83)O_(12-δ)

A solid solution of(HfSc)_(0.83)W_(2.25)P_(0.83)O_(12-δ)is synthesized by the high-temperature, solid-state reaction and fastquenching method. It is shown that it possesses an orthorhombic structure with space group Pmmm(47) and exhibits negative thermal expansion(NTE) property with low anisotropy in thermal expansion. The coefficients of thermal expansion(CTEs) for a, b, and c axes are-1.41 × 10~(-6) K~(-1),-2.23 × 10~(-6) K-1, and-1.87 × 10~(-6) K-1, respectively. This gives rise to volume and linear CTEs of-3.10 × 10-6 K-1 and-1.03 × 10-6 K-1, respectively. Besides, it exhibits also intense photoluminescence from 360 nm to about 600 nm. The mechanism of NTE and the correlation of the PL with axial thermal expansion property are discussed.     

基于微波相位补偿的56 km高精度光纤微波频率传递

报道了实验室内56 km光纤微波频率传递的实验研究,在56 km的传递距离上实现了1.8×10^-15/s,4×10^-18/10⁴s的传递稳定度。系统通过环回法比较往返传递的微波信号相位获得链路上的相位扰动量,并实时控制本地发射端的微波发射信号相位实现预补偿。在环回往返传递的不同方向上,系统方案采用不同频率的微波调制信号,这种方法极大避免了光寄生反射效应的影响,同时利用色散补偿光纤改善探测信号相噪等措施,提高了系统的传递稳定度。     

高准确度的钙离子光频标

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.     

LaTiO高k栅介质Ge MOS电容电特性及Ti含量优化

采用共反应溅射法将Ti添加到La_2O_3中,制备了LaTiO/Ge金属-氧化物-半导体电容,并就Ti含量对器件电特性的影响进行了仔细研究.由于Ti-基氧化物具有极高的介电常数,LaTiO栅介质能够获得高k值;然而由于界面/近界面缺陷随着Ti含量的升高而增加,添加Ti使界面质量恶化,进而使栅极漏电流增大、器件可靠性降低.因此,为了在器件电特性之间实现协调,对Ti含量进行优化显得尤为重要.就所研究的Ti/La_2O_3比率而言,18.4%的Ti/La_2O_3比率最合适.该比率导致器件呈现出高k值(22.7)、低D_(it)(5.5×10~(11)eV~(-1)·cm~(-2))、可接受的J_g(V_g=1V,J_g=7.1×10~(-3)A·cm~(-2))和良好的器件可靠性.     

高Yb3+/Er3+掺杂的磷基有源光纤材料的光谱性质

研究了Yb³⁺/Er³⁺共掺60P₂O₅-15BaO-10Al₂O₃-5ZnO-10R₂O（R=Na,K）以P₂O₅为主体的磷基有源光纤材料的光谱性质,以及不同Yb³⁺/Er³⁺掺杂浓度对光谱性质的影响规律。当Er³⁺浓度为9.100×10¹⁹/cm³、Yb³⁺的掺杂浓度为5.407×10²⁰/cm³、Yb³⁺/Er³⁺浓度比为6：1时,玻璃样品在1 531 nm处的受激发射截面最大,为6.17×10^-21 cm²。同时,其荧光寿命为9.73 ms,荧光半高宽为53.16 nm,发射截面与半高宽的乘积为3.28×10^-32 m³,综合性能最佳。     

锐钛矿金红石的高温原位X射线衍射研究

对TiO₂粉末进行了空气和真空条件下从室温到1200℃的加热原位X射线衍射实验, 得到了空气和真空条件下微米级锐钛矿颗粒转变为金红石的起始温度分别为850℃ 和855℃; 分别修正了空气条件下锐钛矿在(27–850℃)范围和金红石在(900–1200℃) 范围内的晶胞参数和真空条件下锐钛矿在(27–850℃)范围和金红石在(950–1200℃) 范围的晶胞参数, 从而得到了晶胞参数随温度变化的关系, 得到了锐钛矿和金红石在空气中和真空中的热膨胀系数, 并总结了热膨胀系数随温度变化的规律. 室温下锐钛矿在空气条件下的热膨胀系数为 α_a=4.55063×10^-6/℃, α_c=7.7543×10^-6/℃, β=16.85836×10^-6/℃; 真空下为 α_a=4.69429×10^-6/℃, α_c=9.02850×10^-6/℃, β=18.69688×10^-6/℃. 室温下, 金红石在空气条件下的热膨胀系数为 α_a=6.81243×10^-6/℃, α_c=8.71644×10^-6/℃, β=22.22178×10^-6/℃; 真空条件下为 α_a=6.05834×10^-6/℃, α_c= 8.39280×10^-6/℃, β=20.52362×10^-6/℃. 关键词： 2')" href="#">TiO₂ 原位X射线衍射 相转变 热膨胀     

Modeling of cascaded high isolation bidirectional amplification in long-distance fiber-optic time and frequency synchronization system

We propose a physical model of estimating noise and asymmetry brought by high isolation Bi-directional erbiumdoped fiber amplifiers(Bi-EDFAs), no spontaneous lasing even with high gain, in longdistance fiber-optic time and frequency(T/F) synchronization system. It is found that the Rayleigh scattering noise can be suppressed due to the high isolation design, but the amplified spontaneous emission(ASE) noise generated by the high isolation Bi-EDFA and the bidirectional asymmetry of the transmission link caused by the high isolation Bi-EDFA will deteriorate the stability of the system.The calculated results show that under the influence of ASE noise, the frequency instability of a 1200 km system composed of 15 high isolation Bi-EDFAs is 1.773 × 10-13/1 s. And the instability caused by asymmetry is 2.6064 × 10-16/30000–35000 s if the total asymmetric length of the bidirectional link length is 30 m. The intensity noises originating from the laser and detector, the transfer delay fluctuations caused by the variation in ambient temperature and the jitter in laser output wavelength are also studied. The experiment composed of three high isolation Bi-EDFAs is done to confirm the theoretical analysis. In summary, the paper shows that the short-term instability of the T/F synchronization system composed of high isolation Bi-EDFAs is limited by the accumulation of ASE noise of amplifiers and the laser frequency drift, while the long-term instability is limited by the periodic variation in ambient temperature and the asymmetry of the amplifiers.The research results are useful for pointing out the direction to improve the stability of the fiber-optic T/F synchronization system.     

小型化10 MHz恒温晶体振荡器设计

设计了用于高精度铷原子频标的一种小型化恒温压控晶体振荡器.振荡电路采用了稳定性好的并联型皮尔斯电路方案,采用2级?型LC级联滤波器抑制谐杂波,利用互补对称式金属-氧化物-半导体(CMOS)反相器实施隔离.振荡和放大电路选用了低噪声晶体管.晶体的温度控制在频率-温度曲线拐点处.实现了体积为4 mL晶振样件.晶振的短期频率稳定度为1.8?10-12/s,相噪对铷频标频率稳定度的贡献仅为3.2?10-13-1/2.     

Active species in microwave postdischarge for steel-surfacenitriding

Production of nitrogen atoms has been studied in a 2.45-GHz flowing postdischarge in N₂ and N₂-H₂ gas mixtures with Ar as a buffer gas in the high-pressure regime (5×10³ to 6.5×10⁴ Pa). N atom densities have been measured by NO titration in the 10¹⁴-10 ¹⁵ cm³ range and monitored by the first positive emission resulting from the N atom recombination. The rate coefficient of the N+N+N₂ recombination has been found to be _k=6×10^-33 cm⁶ atom^-2 s ^-1 at T₀=300 K, which agrees with previously published data. The N atom production (or degree of N/N₂ dissociation) in front of an Fe-0.1%C substrate correlates well with the thickness of a γ' Fe₄N layer produced by the postdischarge treatment. The H₂ gas was first introduced in the initial phase of treatment to remove surface oxidizing and then was cut off to keep high densities of N atoms. It is deduced that N atoms are more active nitriding species than NH-type radicals     

光纤倏逝波型石英增强光声光谱技术

采用块状光学准直聚焦透镜组的传统石英增强光声光谱(QEPAS)技术存在体积难以缩减,结构稳定性不佳,无法适应空间狭小、振动复杂的特殊环境等缺点.基于此,将光纤倏逝波技术与QEPAS技术相结合,提出了一种新型微纳结构光纤QEPAS痕量气体检测技术.实验中,为了提高QEPAS系统信号幅值,优化了石英音叉与激光束的空间位置、激光波长调制深度,同时对比了两种不同共振频率的石英音叉,最终采用共振频率较低的30.720 kHz石英音叉作为声波探测元件,获得的检测极限为6.25×10~(-4)(体积分数),归一化噪声等效吸收系数为4.18×10~(-7)cm~(-1).W·Hz~(-1/2).     

Monte Carlo simulation of electron swarms in nitrogen in uniformE×B fields

The motion of electrons in nitrogen in uniform E× B fields is simulated using the Monte Carlo technique for 240⩽E/N⩽600 Td (1 Td=1×10^-17 V cm²) and 0⩽B/N⩽0.45×10^-17 T cm³ . The electron-molecule collision cross sections adopted are the same cross sections as those used previously for the numerical solution of the Boltzmann equation. The swarm parameters obtained from the Monte Carlo simulation are compared with the Boltzmann solution and with the experimental data available in the literature. In relation to E×B fields, it is concluded that the Monte Carlo approach provides an independent method of substantiating the validity of the equivalent electric-field approach