计量学专用全金属化4.2K至1.3K液氦杜瓦装置

采用低温超导技术是某些计量学实践中的发展方向。例如在光频测量链中,如以超导腔稳频振荡器(SCSO)作为微波频率源,其短时频率稳定度可达1×10~(12)/10s,这就需要将精密加工的铌腔置于真空的样品室中,而样品室则浸泡在液氦里,通过减压降温过程获得1.3K的温度(腔温可能比液氦高0.04K);这时腔的有载Q值高达1×10~(10),1.3K温度要求长     

短稳标准高Q值超导腔的研究

针对频率标准用超导腔的设计,通过理论分析及编程计算得到了影响微波腔指标的参数,并对不同温度下微波腔的品质因数（Q值）进行计算得到了温度变化曲线,通过此曲线可以确定达到指标所需要的温度。所设计的微波腔参数为：工作模式为TM₀₁₀模式,直径D为60mm,高度l为50mm,频率为4.4GHz,Q值在液氦温度4.2K时达到3.9×10⁷,在减压降温到2K时达到1.9×10⁹,实验结果与计算结果吻合。     

基于光学锁相环的高稳定度激光稳频方法研究

报道了一种基于光学锁相环的高稳定度激光稳频方法,用于提高可调谐外腔半导体激光器(TECDL)的频率稳定度和准确度。自行研制的光学锁相环电路采用数字鉴相与差分运算相结合的方式获得高灵敏度的鉴频鉴相误差信号,并通过高速模拟PID实现整个系统的闭环锁定。利用该光学锁相环系统进行了TECDL偏频锁定至光学频率梳(OFC)的实验,实验结果表明环路锁定后拍频频率波动在±0.3Hz范围内,偏置频率为50MHz时,光学锁相环系统在1s和1000s积分时间的相对阿伦方差分别为1.5×10^-9和8.5×10^-13。系统锁定后,拍频线宽由500kHz压缩至2kHz。该研究表明采用基于光学锁相环的激光稳频方法可以实现亚Hz级的激光频差控制,通过将TECDL偏频锁定至高稳定度的参考激光源可显著提高其频率稳定度,使其能够满足超精密测量、冷原子/离子干涉测量等领域对激光频率稳定度和准确度的要求。     

一种高信噪比铷原子频标物理系统

物理系统是铷原子频标的核心部件,通过分析物理系统原子鉴频信号信噪比对频标频率稳定度的影响机理,对物理系统内部结构进行了改进。改进后的物理系统采用了优化的开槽管微波腔,用Xe气作为起辉气体的铷光谱灯,采用分离滤光的三泡设计方案。对改进后的系统进行了初步测试,秒稳定度约为8×10^-13。此结果表明铷原子频标的稳定度可以突破1×10^-12/τ^(1/2),铷原子频标的长期稳定度还有进一步提高的潜力。     

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。     

锁相环路对氢原子钟性能影响的实验分析

实验以上海天文台SOHM-4型氢原子钟脉泽信号和新研制的模拟-数字混合型锁相环路为基础,主要分析锁相环路参数对氢原子钟输出信号的短期频率稳定度和单边带相位噪声的影响。针对氢脉泽信号高Q值的特殊性,通过理论分析和实验验证寻求与其相匹配的最佳环路参数。实验结果表明,锁相环路的参数设置直接影响到氢原子钟输出信号的性能;在脉泽信号不变的情况下,改进后的锁相环路和主电子学系统可使氢原子钟的频率稳定度提高至1.7×10^-13/1s, 3.3×10^-14/10s, 9.1×10^-15/100s, 2.9×10^-15/1 000s, 1.4×10^-15/10000s,即较之原有的技术指标,在各取样时间范围内,频率稳定度的测试结果均提高了半个量级。     

双纵模稳频He-Ne激光器工作机理及误差分析

为深入分析双纵模稳频氦氖激光器的稳频机理和精度误差,本文提出了双纵模产生的必要条件:内腔型激光器和谐振腔长在100～300 mm之间.按照激光器的工作过程,稳频分为三个阶段:跳模、过渡阶段,模式稳定.结合激光原理和热力学理论,根据光电探测器的电压变化,阐述了稳频机理.拍频实验结果表明,激光器的频率稳定度高达5×10-10.通过误差分析,确定稳频精度仅取决于腔长的变化量,且增加腔长,有助于增加频率稳定度.该方法锁定时间短.     

小型化铷原子频标数字锁频环路设计与实现

设计并实现了一种用于铷原子频标的小型化锁频环路。采用数字锁相倍频技术,实现了10MHz信号的45.5645833次倍频。再经过一级15次倍频后获得频率为6834.6875MHz的铷原子频标微波探寻信号。通过数字电路技术实现了455.645833MHz信号的小调频。测量并分析了455.645833MHz信号的相位噪声,结果表明电路系统对铷频标频率稳定度的贡献为3.2×10^-12τ^-1/2。测量了利用该电路得到的铷频标的短期频率稳定度,结果为5×10^-12τ^-1/2（1s≤τ≤100s）,明显高于一般商品小型化铷原子频标。     

铷原子频标物理系统小型化设计

介绍了一种用于铷原子频标的小型化物理系统。该物理系统采用了开槽管式微波腔和分离滤光设计方案,体积为30 cm³。对该物理系统进行了初步测试,短期频率稳定度为3.8×10^-12/τ^1/2,表明该物理系统同时具备了小型化和高信噪比特点,可以应用于高性能小型化铷原子频标。     

超导腔2K垂直测试低温恒温器的设计

基于中国近年来超导腔的研究及发展趋势,设计了一种新型超导腔2K垂直测试低温恒温器,该恒温器集外真空容器、80 K液氮冷屏、液氦低温杜瓦、2K回冷换热器、J-T阀门以及低温分配与传输为一体.利用恒温器内部回冷提高2K超流氦的产生效率,并且使得相分离器的回流冷量得到充分利用,以最大限度减少2K温度的低温热负荷.     

Hg+ trapped ion standard with the superconducting cavitymaser oscillator

The frequency stability of an atomic standard based on ¹⁹⁹ Hg⁺ ions confined in a hybrid RF/DC linear trap is described. The 40.5-GHz clock transition has been measured to be 17 mHz wide, representing a quality factor greater than 2×10¹². A 160-mHz line is used to steer the output of a 5-MHz crystal oscillator to obtain a stability of 2×10^-15 for 24000-s averaging times. In a separate measurement, a 37-mHz line is used to steer the output of the superconducting cavity maser oscillator to reach 1×10^-15 stability at 10000 s     

Dielectric property measurement system at cryogenic temperature andmicrowave frequencies

A system based on the resonant cavity method has been developed to measure the permittivity and loss tangent at 12-18 GHz over the temperature range 80-300 K. Changes of permittivity as low as 0.01% in the range 1-30, 3x10^-6 for loss tangent values below 10^-2, can be measured without requiring temperature stability. The thermal expansion coefficient and resistivity factor of copper have been measured between 80 K and 300 K. The permittivity of sapphire and loss tangent of alumina of 99.9% purity in the same temperature range are presented     

Flux-locked current source reference

The quantization of flux in a closed superconducting circuit is used to provide a stable reference current. A 10-mA current source is coupled through a toroidal transformer to a DC superconducting quantum interference device (SQUID) input, and the resulting signal is fed back as an error current. The result is a net flux linkage that exhibits short-term stability of 1 part in 10⁹/h. The net current is quantized with a step size of 59.4 nA, and it will exhibit the same stability as the flux provided the mutual inductance of the transformer remains constant. This current is passed through a precise 100-Ω resistor and compared against Zener diode references. The observed temperature coefficient for the flux transformer is 28.5±3 ppm/K at 4.2 K. Possible sources for the temperature dependence are discussed     

Temperature dependence of the growth of gallium oxide on CoGa(100)

The oxidation of a CoGa(100) surface at high temperatures has been studied by scanning tunnelling microscopy (STM) and auger electron spectroscopy (AES). When CoGa(100) is oxidised at a sufficiently high temperature (>600 K), an ordered Ga₂O₃ film is formed. The stability of the film depends on the sample temperature and partial oxygen pressure of the ambient gas. At negligible oxygen pressure (<10⁻¹¹ mbar) the oxide is stable up to 850 K. At an oxygen pressure of 10⁻⁶ mbar the oxide is stable up to 930 K and some of the oxide remains present up to 970 K. The oxide film is found to be very uniform. The thickness of the film is constant and independent of the oxidation temperature (600 K<T<930 K), oxygen pressure (<10⁻⁶ mbar), and exposure (10⁻⁴–10⁻² mbar.s≈10²–10⁴ L). We find a clear improvement of the order of the oxide film surface with increasing oxidation temperature. In STM images, a domain structure of the oxide film is observed. The size of the domains increases by a factor of 5–10 when the oxidation temperature is increased from 700 to 900 K.     

166.6 MHz超导腔加强筋结构的多物理场耦合仿真

高能同步辐射光源加速器的166.6 MHz超导腔采用4.5K饱和液氦浸泡冷却,其内导体与小束管之间设计有加强筋以改善超导的应力分布,加强筋会影响气泡排出,气泡聚集过多会降低液氦冷却效果,有引发失超的风险.使用Fluent、Hfss软件对超导腔内导体附近的流场进行了流动/传热/电磁多物理场耦合仿真,研究了加强筋顶部开孔设...     

变价稀土元素Eu掺杂BiCuSeO热电性能的研究

作为一种适于中温下使用的极具发展前景的新型热电材料, BiCuSeO由于本征热导率低且Seebeck系数较高而广受关注。本研究探索了变价稀土元素Eu替换Bi位对BiCuSeO热电材料微观组织和热电性能的影响。实验结果显示, 样品中同时存在Eu²⁺和Eu³⁺两种价态的离子, 掺杂Eu元素不仅可以增加样品的载流子浓度, 还可以调整样品的能带结构, 进而改善样品的电输运性能, Bi_0.85Eu_0.15CuSeO电导率显著提升, 在823 K时达到了98 S·cm^-1, 相比于未掺杂样品提升了将近6倍。在温度为823 K时, Bi_0.975Eu_0.025CuSeO的功率因子可达0.32 mW·m^-1·K^-2, ZT值为0.49。本研究表明, 掺杂变价稀土元素可以有效改善BiCuSeO热电材料的性能。     

Power stabilized cryogenic sapphire oscillator

Microwave oscillators of exceptional short-term stability have been realized from cryogenic sapphire resonators with loaded Q factors in excess of 10⁹ at 11.9 GHz and 6 K. This has been achieved by a power stabilized loop oscillator with active Pound frequency stabilization. These oscillators have exhibited a fractional frequency stability of 3-4×10^-15 for integration times from 0.3 to 100 s. The relative drift of these two oscillators over one day is a few times 10^-13. To reduce the long-term drift, which is principally due to excessive room temperature sensitivity, we have added cryogenic sensors for the power and frequency stabilization servos to one of these oscillators. We have also implemented a servo to reduce the room temperature sensitivity of our phase modulators. Testing of this oscillator against a Shanghai Observatory H-maser has shown an Allan deviation of 4×10^-15 from 600 to 2000 s     

Temperature-compensated sapphire resonator for ultra-stableoscillator capability at temperatures above 77 K

We report on the design and test of a whispering gallery sapphire resonator for which the dominant (WGH_n11) microwave mode family shows frequency-stable, compensated operation for temperatures above 77 K. The resonator makes possible a new ultra-stable oscillator (USO) capability that promises performance improvements over the best available crystal quartz oscillators in a compact cryogenic package. A mechanical compensation mechanism, enabled by the difference between copper and sapphire expansion coefficients, tunes the resonator to cancel the temperature variation of sapphire's dielectric constant. In experimental tests, the WGH₈₁₁ mode showed a frequency turnover temperature of 87 K in agreement with finite element calculations. Preliminary tests of oscillator operation show an Allan Deviation of frequency variation of 1.4-6×10^-12 for measuring times 1 s ⩽τ⩽100 s with unstabilized resonator housing temperature and a mode Q of 2×10⁶. We project a frequency stability 10^-14 for this resonator with stabilized housing temperature and with a mode Q of 10⁷     

Microwave penetration depth measurement for high Tcsuperconductors by dielectric resonators

The penetration depth λ(T) dependence on temperatures for high T_c superconducting YBa₂Cu₃O_7-δ thin films stored in various environments was measured by a well-designed microwave dielectric resonator. A d-wave T² dependence was observed at low temperatures, while an exponential dependence of the penetration depth λ(T) relevant to the s wave was detected as temperature increases due to thermal fluctuation. An abnormal upturn of the penetration depth at temperatures below 10 K attributed to the surface current carried by the defect surface-induced Andreev bound states can be apparently observed without applying heavy-ion bombardment from this relatively higher frequency measurement. Readers who endeavor to start this kind of measurement can use the well-modified dielectric cavity in conjunction with the detailed measuring procedure