CO2/OsO4 lasers as frequency standards in the29 THz range

The CO₂ lasers, frequency stabilized on OsO₄ transitions around 29 THz, are successfully used as secondary references for visible frequency synthesis and also for high-accuracy spectroscopy in the infrared domain. The BNM-LPTF CO₂/OsO₄ frequency standards exhibit high metrological performances: a long term reproducibility of ±10 Hz (1σ=2×10^-13) and a stability σ_y=6.6×10^-14/√τ with a Flicker plateau of 4×10^-15 (Δν/ν=0.1) for 300 s to 10³ s averaging times. These results and a preliminary study of the main effects which can induce frequency shifts are reported     

磷酸处理对多孔SiO2薄膜质子导电特性和双电层薄膜晶体管性能的影响

采用等离子体增强化学气相沉积法(PECVD)制备了多孔SiO₂薄膜, 系统地研究了不同浓度磷酸处理对多孔SiO₂薄膜的质子导电特性、双电层电容和以此多孔SiO₂薄膜为栅介质的铟锌氧(IZO)双电层薄膜晶体管性能的影响。结果表明: 多孔SiO₂薄膜的质子电导率和双电层电容随磷酸浓度升高而增大, 60%浓度磷酸处理后多孔SiO₂薄膜质子电导率和双电层电容分别达到1.51×10^-4 S/cm和6.33 μF/cm²。随磷酸浓度升高, 双电层薄膜晶体管的工作电压降低, 并且, 电流开关比也变大。其中60%浓度磷酸处理后器件工作电压为1.2 V, 迁移率为20 cm²/(V·s), 电流开关比为4×10⁶。这种双电层薄膜晶体管有望应用在化学和生物传感等领域。     

Very high Q microwave spectroscopy on trapped171Yb+ ions: application as a frequency standard

A microwave frequency standard based on buffer-gas cooled ¹⁷¹ Yb⁺ ions confined in a linear Paul trap has been demonstrated in prototype form. The standard exhibits a fractional frequency instability characterized by an Allan deviation σ_y (τ)=3.7×10^-13τ^-1/2 for τ<3000 s. Microwave Ramsey fringes with a Q factor of 1.5×10¹³ have been observed     

Measurements of the complex dielectric constant of sand and dustparticles at 11 GHz

Measurements are reported of the refractive index (Δn ) and loss tangent (tan δ) of dust particles in a laboratory-simulated model of dust storms, carried out at 11 GHz utilizing a confocal microwave open-cavity resonator. Four samples were used, namely, sandy, silty, clayey silt, and clayey, for concentrations varying from 10^-4 to 4×10^-3 g/cm³. The particle-size distribution (PSD) of each sample was measured using the hydrometer technique. Dielectric-constant measurements were also conducted at bulk concentrations using the standing-wave technique for the dry samples and as a function of volumetric moisture content for up to 0.5 cm³/cm³. The complex dielectric constant of the dust particle material was evaluated by two approaches. In one the data for permittivities obtained over the whole range of measured concentrations were extrapolated to the particle densities of the samples. In the other a mixing formula was utilized for the determination of ε_s from permittivities measured at bulk concentrations     

High-accuracy time transfer via geostationary satellites:preliminary results

Signal-delay phase measurements have been performed with Ku-band Earth station and VSAT (very-small-aperture terminal) facilities in various loop-around schemes using both a satellite simulator and geostationary satellites. Stability plots show that the standard deviation of pair differences (σ_y) is 4×10^-10 _τ^-1 for a C/No (carrier-to-noise density) ratio of 65 dB-Hz. This white-noise behavior continues for several days, when satellite simulator data shows σ _y to be 3×10^-15. Absolute phase-delay measurements show reproducibility to better than 1 ns over a 16-day sample time. This suggests the potential for accuracy to this level, given an appropriate calibration. A measurement method is described which determines the principal time-delay constant affecting the accuracy of time synchronization using a two-way satellite communications technique     

Reducing local oscillator phase noise limitations on the frequencystability of passive frequency standards: tests of a new concept

We report on the experimental test of a new concept for reducing the limitation on short-term frequency stability of passive frequency standards due to local oscillator phase noise. This concept is general and can be applied to many passive frequency standards. Systems that use sinewave modulation to interrogate a stable resonance are limited in short-term frequency stability by phase noise at the second harmonic of the modulation, f_m. This effect limits the fractional frequency stability to approximately σ_v(τ7)=0.9(f _m/ν₀) (S_φ(2f_m))^1/2τ^-1/2, where ν₀ is the carrier frequency and S_φ(2f _m) is the phase noise at twice the modulation frequency. (Contributions from higher even harmonics of the modulation generally can be neglected). This new concept uses notch filters at ±2f_m from the carrier to reduce this effect. Tests on a modified passive rubidium standard demonstrate an improvement of approximately 18 in σ_y(τ). The dual notch filters proved to be feasible and were obtained commercially. Measurements suggest that ultimate performances of less than 2×10^-14τ^-1/2 are possible if the atomic resonance has sufficient quality     

Widely extended new method for measuring the impedance (CxRx) at high frequencies withapplications

A method is described for the accurate measurement of the equivalent parallel capacitance C_x and resistance R_x of very high loss materials at high frequencies. The important characteristic of the method is its capability of measuring the value of C_x extending from 10^-2 to 10⁶ pF and R_x from 10 to 100×10⁶ Ω. The authors measure the humidity of tea leaves and rockwool by measuring the capacitance C_x of specimens irrespective of the value of R_x     

A new low-field determination of the proton gyromagnetic ratio inwater

The proton gyromagnetic ratio in water has been measured by the low field method using atomic magnetic resonance in ⁴He, a multicurrent solenoid and an induction method for the dimensional measurement of the solenoid. The result for air and vacuum environment is γ'_p (low, air)=2.67515451×10⁸ s^-1 T^-1 (0.18×10^-6), γ'_p (low, vacuum)=2.67515418×10⁸ s^-1 T^-1 (0.18×10^-6), based on the adopted values K_J-90=483597.9 GHz/V, R_K-90=25812.807 Ω, and measured values γ(⁴ He)/γ'_p=658.200556, γ(⁴He) (air)=1760.78819×10⁸ s^-1 T^-1 (0.18×10^-6), K_J-90, R_K-90     

Impact of new clock technologies on the stability and accuracy ofthe International Atomic Time TAI

The BIPM Time Section is in charge of the generation of the reference time scales TAI (International Atomic Time) and UTC (Coordinated Universal Time). Both time scales are obtained in deferred-time by combining the data front a number of atomic clocks spread worldwide. Since the end of 1992, the quality of the timing data received at the BIPM has evolved rapidly thanks to the extensive replacement of older designs of commercial cesium clocks by the new HP 5071A units and to the use of active auto-tuned hydrogen masers. Consequently, the stability and the predictability of the reference time scales has improved significantly: these are characterized by an Allan standard deviation σ_y(τ) of 2.6×10^-15 for averaging times τ=40 d. The accuracy of TAI is estimated by the departure between the duration of the TAI scale interval and the SI second as produced on the rotating geoid by primary frequency standards. It is now possible to estimate TAI accuracy through the combination of results obtained from six different primary standards: LPTF-FO1, PTB CS1, PTB CS2, PTB CS3, NIST-7, and SU MCsR 102, all corrected for the black-body radiation shift. This led to a mean departure of the TAI scale interval of +2.0×10^-14 s over 1995, known with a relative uncertainty of 0.5×10^-14 (1 σ)     

Experimental determination of the gyromagnetic ratio of thehelium-4 atom in terms of that of the helium-3 nucleus

The ratio R=γ_4He(2³S₁)/γ_3He (1¹S₀) has been measured using gaseous samples in low magnetic field. The result, R=864.02276±3×10 ^-8, leads to a value of γ_4He=1760.78798(3×10^-7)×10⁸ ×rad×s^-1×T^-1     

铝酸盐的组成对钡钨阴极性能的影响

采用液相共沉淀法制备了612铝酸盐(n(BaO):n(CaO):n(Al₂O₃)=6:1:2)前驱粉末, 在不同气氛(H₂、CO₂、N₂)、不同温度(1300℃、1400℃、1500℃)焙烧制备铝酸盐, 系统研究了不同工艺制备的铝酸盐对钡钨阴极性能的影响。结果表明: 前驱粉末的最佳焙烧工艺为: H₂气氛、1500℃, 可获得主相为Ba₅CaAl₄O₁₂的铝酸盐, 用其制备的钡钨阴极发射电流密度可达12.2 A/cm², 蒸发速率仅为1.09×10^-8 g/(cm²?s)。     

MnO2纳米棒-还原石墨烯复合修饰玻碳电极用于苋菜红的检测

利用电化学还原法制备MnO₂纳米棒-还原石墨烯复合修饰电极（MnO₂ NRs-ErGO/GCE）用于苋菜红的检测。采用SEM和XRD分别对修饰电极材料进行微观形貌和成分结构表征。通过循环伏安法考察了苋菜红在裸电极、ErGO/GCE和MnO₂ NRs-ErGO/GCE上的电化学行为,并对测定条件如pH值、富集电位、富集时间进行了优化。结果表明,MnO₂ NRs-ErGO增大了GCE电化学活性面积,提高了苋菜红的电化学氧化响应。在最优的检测条件下,MnO₂ NRs-ErGO/GCE线性扫描伏安法检测苋菜红线性范围为2.0×10^-8~1.0×10^-5 mol/L和1.0×10^-5~4.0×10^-4 mol/L,检测限为1.0×10^-8 mol/L。MnO₂ NRs-ErGO/GCE用于真实饮料样品检测,获得满意结果。     

溶胶-凝胶法制备Al3+、Yb3+掺杂石英光纤纤芯的研究

以正硅酸乙酯、氯化铝和氯化镱为前驱体, 用溶胶-凝胶法制备了Al³⁺、Yb³⁺掺杂石英光纤纤芯。采用ICP-AES分析发现: 碱催化的掺杂硅凝胶上下层组分存在较大差异, 酸催化条件能够消除组分差异。将酸催化溶胶经凝胶化、热处理、玻璃化、光学加工, 获得了φ2.5 mm×50 mm的芯棒。测试2 mm厚芯棒玻璃的光谱和荧光寿命, 1020 nm的荧光寿命为896 μs, 羟基含量为0.4×10^-6, 并通过显微拉曼光谱分析玻璃结构。采用管棒法制备预制棒, 2000℃高温拉制了Al³⁺、Yb³⁺掺杂单包层石英光纤。用光纤折射率分布测试仪测得纤芯折射率波动Δn小于2×10^-4, 表明纤芯具有良好的光学均匀性。本研究结果提供了一种大模场掺镱石英光纤纤芯材料的制备方法, 并为溶胶-凝胶法制备均匀多组分材料的研究提供了理论参考。     

Thickness dependence of electrical properties of PZT films deposited on metal substrates by laser-assisted aerosol deposition

Dependence of electrical properties-dielectric, ferroelectric, and piezoelectric properties-on film thickness was studied for lead-zirconate-titanate (PZT) thick films directly deposited onto stainless-steel (SUS) substrates in actuator devices by using a carbon dioxide (CO₂), laser-assisted aerosol deposition technique. Optical spectroscopic analysis data and laser irradiation experiments revealed that absorption at a given wavelength by the film increased with increasing film thickness. Dielectric constant epsiv, remanent polarization value P_r, and coercive field strength E_c of PZT films directly deposited onto a SUS-based piezoelectric actuator substrate annealed by CO₂ laser irradiation at 850degC improved with increasing film thickness, and for films thicker than 25 mum, e > 800, Pr > 40 muC/cm², and E_c < 45 kV/cm. In contrast, the displacement of the SUS-based actuator with the laser-annealed PZT thick film decreased with increasing film thickness.     

Determination of the time-dependence of ΩNBS usingthe quantized Hall resistance

The quantum Hall effect is being used to monitor the US legal representation of the ohm, or as-maintained ohm, Ω_NBS. Measurements have been made on a regular basis since August 1983. Individual transfers between the quantized Hall resistance R _H and the five 1-Ω resistors which comprise Ω_NBS can be made with a total of one standard deviation (1σ) uncertainty of ±0.014 p.p.m. This uncertainty is the root-sum-square of 32 individual components. The time-dependent expression for R_H in terms of Ω_NBS is: R_H=25812.8[1+(1.842±0.012)×10^-6 =(0.0529±0.0040)(t-0.7785)×10^-6 /year] Ω_NBS, where t is measured in years from January 1, 1987. The value of Ω_NBS is, therefore, decreasing at the rate of (0.0529±0.0040) p.p.m./year     

Comparison of quantized Hall resistances RH(2) andRH(4) of a GaAs/AlGaAs heterostructure device

Quantized Hall resistances R_H(4) and R_H(2) of a GaAs/AlGaAs heterostructure were compared with reference resistors whose values are close to h/4e² or h/2e². The values of the reference resistors were compared with a 100 ohm standard resistor via a cryogenic current comparator (CCC) resistance bridge. Results showed that (4×R_H(4)-2×R_H(2))/2×R_H (2)=(0.037±0.019)×10^-6     

导管对圆柱共鸣腔径向共振模式的扰动

修正进气导管的影响对声学共鸣法测量Boltzmann常数kB十分必要。基于一阶声学微扰理论研究了导管对圆柱形共鸣腔理想径向共振模式的扰动,分析了导管末端不同连接方式所带来的声阻抗差异,计算了导管对（001）径向模式的共振频率和半宽的扰动值分别为Δf/f0≈-0.04×10^-6和Δg/f0≈14.15×10^-6,同时分析了导管长度、半径以及径向安装位置的变化对理想径向共振模式扰动的影响。     

High spectral purity CO2 laser stabilized using amolecular frequency reference

A CO₂ laser has been frequency stabilized to a molecular absorption line with a bandwidth of 10 kHz, yielding a laser noise spectral density reduction below 1 Hz/√ Hz and a relative accuracy of 10^-10. In the time domain, this corresponds to an Allan standard deviation of σ(2, τ)=3·10^-14 τ^-1/2, for τ>100 μs. This source allows experiments of very high resolution spectroscopy as well as the realization of accurate frequency standards in the 10-μm region     

(H4N)2S对电合成CoO/聚苯胺复合膜腐蚀性能的影响

在CoSO₄-C₆H₇N-H₂SO₄混合液中,采用恒电位法合成了CoO/聚苯胺（PANI）复合膜,研究了添加剂（H₄N）₂S对CoO/PANI复合膜的影响。通过电化学测试技术、SEM、XRD和加速腐蚀试验等方法对CoO/PANI复合膜的微观形貌及耐腐蚀性能进行分析。结果表明,合成的CoO/PANI复合膜中,CoO以晶体形式存在,（H₄N）₂S的加入改变了CoO/PANI复合膜膜层的微观形貌,由不致密不规则的片状结构转变为均匀致密规则的片状一体结构,（H₄N）₂S加入量过大导致（H₄N）₂S-CoO/PANI复合膜表面出现少量孔洞;未添加（H₄N）₂S的CoO/PANI复合膜自腐蚀电流密度为7.079×10-6 A/cm2,自腐蚀电位为-0.545 V,添加0.3 g/L的（H₄N）₂S后,（H₄N）₂S-CoO/PANI复合膜自腐蚀电流密度达到7.943×10-7 A/cm2,自腐蚀电位达到-0.314 V,极化电阻为6 426.8 Ωcm2,经过10% HCl点滴腐蚀时间达478 s,中性盐雾实验56 h未见锈蚀,（H₄N）₂S显著提高了CoO/PANI复合膜的耐腐蚀性能。