高温超导台阶结YBCO dc-SQUID一阶平面梯度计

在10mm×10mm SrTiO₃(STO)台阶衬底上用单层YBa₂Cu₃ O_7-δ(YBCO)薄膜制备了dc-SQUID一阶平面梯度计,探测环面积约为33mm ²,基线长度d=45mm.该梯度计在无屏蔽条件下对地磁场有较好的屏蔽作用,共模抑 制比为14×10²,磁场梯度灵敏度为8PT/cmHz(白噪声区). 关键词： 台阶结 SQUID 平面梯度计     

大有效面积的高Tc rf SQUID

关键词： c rf SQUID')" href="#">高T_c rf SQUID 新型结构 大有效面积 磁通聚焦器     

Oxygen-defects-related dielectric response in CaCu3Ti4O12 ceramics

A 10 mm thickness columned CaCu₃Ti₄O₁₂ ceramic was fabricated by the conventional solid-state reaction method and the dielectric properties of different parts in ceramic had been investigated. For the sample close to the surface, only one Debye-type relaxation around 10⁷ Hz was observed at room temperature. However, for the sample close to the core, another relaxation peak was observed at about 10⁴ Hz. The results were explained in terms of the equivalent circuit model by showing in the impedance spectroscopy. Moreover, it was introduced that the low-frequency dielectric relaxation is associated with the electrode-sample contact effect based on varying sample thickness and an annealing treatment in the nitrogen atmospheres.     

非晶态软磁薄膜Fe90-xCoxZr10的平面霍耳效应和磁阻效应

本文研究了非易态软磁薄膜Fe_90-xCo_xZr₁₀的平面霍耳电压及磁阻随磁场方向、成分和温度的变化规律。采用通常的六探针法进行了测量。结果表明平面霍耳电压和磁阻分别满足经验公式V_y=pM²Isin2θ和△ρ=cM²cos2θ;并给出了V_y表达式中的常数项p正比于ρ²。此外,样品Co₉₀Zr₁₀和样品Fe₇₀Co₂₀Zr₁₀晶化前后的V_y变化正好相反,即富钴成分的样品晶化后,V_y增加,而富铁成分的样品V_y下降。 关键词：     

利用高温超导直流量子干涉器件进行10$lt;sup$gt;-6$lt;/sup$gt; T量级磁场下核磁共振的研究

研究了水样品在10^-6 T量级磁场下的核磁共振谱.核磁共振信号由一个工作在液氮温度的高温超导直流量子干涉仪记录,测量在一个简易磁屏蔽室中进行.在7—70 μT的磁场范围内都观察到了15 ml水样品的核磁共振信号.相应的^1H的核磁共振频率为300—3000 Hz.在实验中获取的单次测量信噪比约为4,通过对信号的100次平均,信噪比可达到约40.进一步讨论了剩余磁场、预极化时间和采样时间对结果的影响.最后用数字滤波之后平均的方法初步得到了时域的自由感应衰减信号. 关键词： 超导量子干涉仪 核磁共振     

A contrastive study on the influences of radial and three-dimensional satellite gravity gradiometry on the accuracy of the Earth's gravitational field recovery

The accuracy of the Earth’s gravitational field measured from the gravity field and steady-state ocean circulation explorer(GOCE),up to 250 degrees,influenced by the radial gravity gradient V zz and three-dimensional gravity gradient V ij from the satellite gravity gradiometry(SGG) are contrastively demonstrated based on the analytical error model and numerical simulation,respectively.Firstly,the new analytical error model of the cumulative geoid height,influenced by the radial gravity gradient V zz and three-dimensional gravity gradient V ij are established,respectively.In 250 degrees,the GOCE cumulative geoid height error measured by the radial gravity gradient V zz is about 2 1/2 times higher than that measured by the three-dimensional gravity gradient V ij.Secondly,the Earth’s gravitational field from GOCE completely up to 250 degrees is recovered using the radial gravity gradient V zz and three-dimensional gravity gradient V ij by numerical simulation,respectively.The study results show that when the measurement error of the gravity gradient is 3×10 12 /s 2,the cumulative geoid height errors using the radial gravity gradient V zz and three-dimensional gravity gradient V ij are 12.319 cm and 9.295 cm at 250 degrees,respectively.The accuracy of the cumulative geoid height using the three-dimensional gravity gradient V ij is improved by 30%-40% on average compared with that using the radial gravity gradient V zz in 250 degrees.Finally,by mutual verification of the analytical error model and numerical simulation,the orders of magnitude from the accuracies of the Earth’s gravitational field recovery make no substantial differences based on the radial and three-dimensional gravity gradients,respectively.Therefore,it is feasible to develop in advance a radial cold-atom interferometric gradiometer with a measurement accuracy of 10 13 /s 2-10 15 /s 2 for precisely producing the next-generation GOCE Follow-On Earth gravity field model with a high spatial resolution.     

Equivalent magnetic noise in magnetoelectric Metglas/Pb(Mg1/3Nb2/3)O3‐PbTiO3 laminate composites

We have experimentally and theoretically investigated the equivalent magnetic noise in a magnetoelectric Metglas/ 0.7Pb(Mg_1/3Nb_2/3)O₃‐0.3PbTiO₃ laminate sensor unit by considering the constituent noise sources of dielectric loss (N_DE) and DC leakage resistance (N_R). In the low frequency range (f = 1 Hz), theory predicts that N_R dominates the noise charge (1.6 times larger than N_DE), with a 1 Hz noise of 9.1\;{\rm pt}/\sqrt {\rm Hz}. The experimental equivalent magnetic noise was 10.8\;{\rm pt}/\sqrt {\rm Hz}. This observed value is slightly higher than the predicted one, which might be due to an oversimplification of the theoretical model in terms of electrical charge amplifier and external vibration noise sources. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Initial operation at liquid-helium temperature of the M =2270 kg Al 5056 gravitational-wave antenna of the Rome group

Summary We report on the cooling at liquid-helium temperature of our 2270 kg 5056 Al bar at CERN. The liquid-helium container had been filled up to 1500 liters ensuring to keep the antenna cold for more than one month. The antenna is equipped with a resonant capacitive transducer operating at constant electrical charge with a FET low-noise amplifier. The transducer is tuned to the antenna within less than I Hz and the two normal-mode frequencies are ν₋=908.160 Hz and ν₊=924.234 Hz with an applied electrical field in the transducer of 10⁶ V/m. The corresponding overall merit factors areQ ₋=5.20·10⁶ andQ ₊=7.25·10⁶. The transducer has been tested up to an electrical field of 6·10⁶ V/m: in this condition we have βQ≈10⁴. The antenna has been in operation for several weeks giving, for the Brownian noise, values in agreement with the calculated values. We report also on the results of tests performed on a DC SQUID, whose input was connected to a commercial capacitor via a transformer with turn ratio of 1000. Supported in part by Japan Society for the Promotion of Science.     

VCSEL based Faraday rotation spectroscopy with a modulated and static magnetic field for trace molecular oxygen detection

Faraday Rotation Spectroscopy (FRS) is a useful technique for quantification of paramagnetic trace gases with significantly higher sensitivity when compared to direct absorption techniques. Our prototype system based on the openPHOTONS sensor core measures the concentration of molecular oxygen (O₂) in the A band using a 763-nm vertical cavity surface emitting laser. We provide detailed analysis of two measurement methods based on FRS using the same sensor configuration: one with a modulated magnetic field, and one with a static magnetic field in combination with wavelength modulation. Our spectra signal-to-noise ratios agree well with our simulations via modeling of the FRS signal. For alternating magnetic field, we achieve an equivalent minimum detectable absorption (MDA) of 8.86×10^-7/Hz^\frac128.86\times 10^{-7}/\mathrm{Hz}^{\frac{1}{2}} resulting in a minimum detection limit of 30 ppmv⋅m/ Hz^\frac12\mathrm{Hz}^{\frac{1}{2}} of O₂, limited by detector noise and laser noise. For the same system configuration in the static field case, parasitic etalon fringes limited the MDA to 4.8×10^-6/Hz^\frac124.8\times 10^{-6}/\mathrm{Hz}^{\frac{1}{2}}. In both cases, we describe methods to improve signal-to-noise ratio based on our data and models.     

YBaCuO BICRYSTAL JUNCTIONS AND DC SUPERCONDUCTING QUANTUM INTERFERENCE DEVICES

We have prepared yttria-stabilized-zirconia bicrystal substrates using a simple hot-pressing method. The grain-boundary junctions have been fabricated with YBa₂Cu₃O₇ thin films grown epitaxially on the bicrystals. The patterns are defined by conventional photolithography, The dc and microwave characteristics of the junctiorts and the dc superconducting quantum interference devices (SQUIDs) have been intensively studied. The current-voltage curves are bridge-typed with noise rounding near the critical current. Resistive tail has been observed in the resistance versus temperature curves. The results are compared with the theoretical prediction for classical Josephson junctions. It is found that the behavior of bicrystal junctions can be described in the frame of classical theory. The deviations are attributed to the nonuniformity of the junctions. The small loop dc SQUIDs demonstrate diffraction and interference effects with regard to the applied magnetic field. A large square-washer with a new configuration has been designed to enhance the effective area of dc SQUID as a magnetometer. It has achieved a magnetic field resolution down to 1 pT/(Hz)^1/2(at 10Hz) at 77K.     

Bandbreite im Threshold-Bereich des 0.63 μ He/Ne-Lasers

A double laser device of high stability was used to determinate the threshold bandwidth of a He/Ne-laser amplifier and oscillator. I. Using one laser as a single-mode oscillator, the other as an amplifier, resonance curves of the amplifier with bandwidths between_IΔv=2.5 · 10³ and 1.7 · 10⁶ Hz were recorded. II. Operating the two lasers as single-mode oscillators, beat frequencies with a bandwidth_IIΔv?100 Hz were observed. Extrapolating these results to the threshold noise power the threshold-bandwidths_IΔv _R ^* =1.4 · 10³ Hz and_IIΔv _R ^* =2.0 · 10³ Hz, respectively, are obtained.     

A high-stability semiconductor laser system for a <Superscript>88</Superscript>Sr-based optical lattice clock

We describe a frequency-stabilized diode laser at 698 nm used for high-resolution spectroscopy of the ¹S₀–³P₀ strontium clock transition. For the laser stabilization we use state-of-the-art symmetrically suspended optical cavities optimized for very low thermal noise at room temperature. Two-stage frequency stabilization to high-finesse optical cavities results in measured laser frequency noise about a factor of three above the cavity thermal noise between 2 Hz and 11 Hz. With this system, we demonstrate high-resolution remote spectroscopy on the ⁸⁸Sr clock transition by transferring the laser output over a phase noise-compensated 200-m-long fiber link between two separated laboratories. Our dedicated fiber link ensures a transfer of the optical carrier with frequency stability of 7×10⁻¹⁸ after 100 s integration time, which could enable the observation of the strontium clock transition with an atomic Q of 10¹⁴. Furthermore, with an eye toward the development of transportable optical clocks, we investigate how the complete laser system (laser+optics+cavity) can be influenced by environmental disturbances in terms of both short- and long-term frequency stability.     

Well-confined Yb:GdVO4 laser waveguide formed by MeV C ion implantation

The planar waveguide in x-cut Yb:GdVO₄ crystal has been fabricated by 6.0 MeV carbon ion implantation with the fluence of 1 × 10¹⁴ ions/cm² at room temperature. The modes of the waveguide were measured by the prism-coupling method with the wavelength of 633 nm and 1539 nm, respectively. An enhanced ordinary refractive index region was formed with a width of about 4.0 μm beneath the sample surface to act as a waveguide structure. By performing a modal analysis on the observed transverse magnetic polarized modes, it was found that all the transverse magnetic polarized modes can be well-confined inside the waveguide. Strong Yb-related photoluminescence in Yb:GdVO₄ waveguide has been observed at room temperature, which reveals that it exhibits possible applications for integrated active photonic devices.     

Improved absolute frequency measurement of the 115In+ 5s2 1S0-5s5p3P0 narrowline transition: Progress towards an optical frequency standard

We report on an improved absolute frequency measurement of the 5s ^{2 1} S ₀0-5s5p ³ P ₀ narrowline clock transition at 236.5 nm, for a single, trapped, and laser-cooled ¹¹⁵In ion. Using a narrowline laser as the local oscillator, a linewidth of 43 Hz for the transition is resolved. The uncertainty of the transition frequency’s centroid is 18 Hz, leading to a fractional uncertainty of 1.4 × 10⁻¹⁴. For absolute frequency measurement, we use an optical frequency comb locked to a cesium clock as the reference. The transition frequency is found to be 1267402452900967(63) Hz, averaged over 13 days of separate measurements. The accuracy is about 5.0 × 10⁻¹⁴. We discuss possibilities for further improvement. Original Text ? Astro, Ltd., 2007.     

Superparamagnetic behavior of La0.67Sr0.33MnO3 nanoparticles prepared via sol-gel method

Magnetic nanoparticles of La_0.67Sr_0.33MnO₃ (LSMO) manganite were prepared by sol-gel method. Phase formation and crystal structure of the synthesized powder were examined by the X-ray diffraction (XRD) using the Rietveld analysis. The mean particle size was determined by the transmission electron microscopy (TEM). Infrared transmission spectroscopy revealed that stretching and bending modes are influenced by calcinations temperature. The temperature dependence of the ac magnetic susceptibility was measured at different frequencies and ac magnetic fields in the selected ranges of 40-1000 Hz and 80-800 A/m, respectively. The temperature dependence of ac susceptibility shows a characteristic maxima corresponding to the blocking temperature near room temperature. The frequency dependence of the blocking temperature is well described by the Vogel-Fulcher law. By fitting the experimental data with this law, the relaxation time τ₀=1.7×10⁻¹² s, characteristic temperature T₀=262±3 K, anisotropy energy E_a/k=684±15 K and effective magnetic anisotropy constant k_eff=2.25×10⁴ erg/cm³ have been obtained. dc Magnetization measurement versus magnetic field shows that some of LSMO nanoparticles are blocked at 293 K. The role of magnetic interparticle interactions on the magnetic behavior is also investigated.     

Improvement of magnetic intergranular isolation and evaluation of read/write characteristics on SmCo5 perpendicular magnetic thin films

SmCo₅ alloy is a promising candidate for ultra-high-density perpendicular magnetic recording (PMR) media because of its high uniaxial magnetocrystalline anisotropy K_u of more than 1.1×10⁸ erg/cm³. Previously, we successfully achieved high K_u in a sputter-deposited SmCo₅ thin film by introducing a Cu/Ti dual underlayer. However, in order to apply the SmCo₅ films to practical PMR media, it is necessary to decrease medium noise. A granulated magnetic film comprising of small and magnetically decoupled grains is effective in reducing the medium noise. In this paper, we have proposed a new granular film that is fabricated by partial thermodiffusion of Cu between the Sm-Co continuous layer and the Cu underlayer, which is granulated using compositional segregation caused by the addition of Ta₂O₅. We have analyzed the magnetic properties, magnetic domain size, and magnetization reversal process of the proposed SmCo₅ film. The magnetic domain size decreased and the magnetization reversal process changed from the magnetic-wall-motion mode to a coherent rotation mode to some extent on isolation of magnetic grains. The read/write characteristics of granulated SmCo₅ double-layered media were also evaluated. The medium noise decreased and the signal-to-noise ratio increased for the granulated double-layered (PMR) medium.     

Adaptive noise cancellation in neuromagnetic measurement systems

Summary The noise spectrum of a superconducting second-derivative gradiometer has been investigated in an urban environment. Data have been acquired from the gradiometer with three orthogonal accelerometers and a triaxial fluxgate magnetometer attached to the dewar. These data have been analyzed by using signal processing techniques, primarily an adaptive noise canceller, to reduce noise in the gradiometer data. Results shown here indicate that the environmental noise and/or the dewar motion noise can be reduced as much as 40 dB in noise power. It is also shown, in the case of poor signal-to-noise ratio (S/N∼1), that a 10 Hz sine wave can be extracted. This technique not only shows promise for noise reduction, but also aids in the identification of noise signals which might be misconstrued as part of the evoked response. Analysis of data containing evoked response is now underway. Paper presented at the ?IV International Workshop on Biomagnetism?, held in Rome, September 14–16, 1982.     

Optical-feedback cavity-enhanced absorption spectroscopy with a quantum-cascade laser yields the lowest formaldehyde detection limit

We report on the first application of Optical Feedback-Cavity Enhanced Absorption Spectroscopy to formaldehyde trace gas analysis at mid-infrared wavelengths. A continuous-wave room-temperature, distributed-feedback quantum cascade laser emitting around 1,769 cm^?1 has been successfully coupled to an optical cavity with finesse 10,000 in an OF-CEAS spectrometer operating on the ν₂ fundamental absorption band of formaldehyde. This compact setup (easily transportable) is able to monitor H₂CO at ambient concentrations within few seconds, presently limited by the sample exchange rate. The minimum detectable absorption is 1.6 × 10^?9 cm^?1 for a single laser scan (100 ms, 100 data points), with a detectable H₂CO mixing ratio of 60 pptv at 10 Hz. The corresponding detection limit at 1 Hz is 5 × 10^?10 cm^?1, with a normalized figure of merit of 5 × 10^?11cm $^{-1}/\sqrt{\rm Hz}$ (100 data points recorded in each spectrum taken at 10 Hz rate). A preliminary Allan variance analysis shows white noise averaging down to a minimum detection limit of 5 pptv at an optimal integration time of 10 s, which is significantly better than previous results based on multi-pass or cavity-enhanced tunable QCL absorption spectroscopy.     

Short-term frequency stabilization of diode-laser-pumped Nd:YAG lasers using double-pendulum suspended cavities

We describe the improvement of short-term frequency stability of diode-laser-pumped Nd:YAG lasers. To improve the vibrational isolation of reference cavities, the reference cavities were suspended by a double pendulum with magnetic damping. The frequency noise was reduced to lower than 1 Hz/Hz at Fourier frequencies higher than 5 Hz and the minimum noise of 7 × 10^–3 Hz/Hz was recorded. The minimum root Allan variance was about 10^–14 for the sampling time of 0.01 s. Heating of the reference cavity by absorbed laser power caused the thermal drift of cavity resonance frequencies. It resulted in the laser linewidth in the range of 30–50 Hz.     

Influence of the noise driving force on the diffusion of copper in aluminium thin films

The diffusion of copper in thin polycrystalline aluminium films subjected to current stressing at 140 C was studied. Experimental aluminium stripes were doped with copper in a limited (source) region and the movement of copper away from this region was investigated by electron probe microanalyser. Samples were stressed both by dc and by superimposed dc and noise current. The dc density (5×10⁵ A/cm²) was equal to that of the effective (r.m.s.) value of superimposed current. The frequency range of the noise signal with the Gaussian distribution of amplitudes was 5 Hz to 20 kHz. Under the described conditions copper diffused due to the concentration gradient as well as the electromigration driving force. The diffusion coefficients of copper at both current stressings were obtained by fitting the measured concentration profiles to those calculated theoretically. The results yield that the diffusion becomes enhanced when the noise is applied. The values of thermal grain boundary-assisted diffusion coefficient obtained in six independent measurements with dc loading vary betweenD _Tb=8×10^–13 cm²/s and 25×10^–13 cm²/s. The corresponding values of total diffusion coefficient (i.e. the sum of the thermal and noise induced component) areD _b=(20÷83)×10^–13 cm²/s. The noise-induced enhancement of the diffusion was predicted theoretically. Thus, the present results confirm the previous theoretical calculations.The authors wish to thank Dr. V. Bezák for stimulating discussions.