Versatile cold atom target apparatus

We report on a compact and transportable apparatus that consists of a cold atomic target at the center of a high resolution recoil ion momentum spectrometer. Cold rubidium atoms serve as a target which can be operated in three different modes: in continuous mode, consisting of a cold atom beam generated by a two-dimensional magneto-optical trap, in normal mode in which the atoms from the beam are trapped in a three-dimensional magneto-optical trap (3D MOT), and in high density mode in which the 3D MOT is operated in dark spontaneous optical trap configuration. The targets are characterized using photoionization.     

An efficient magneto-optical trap of metastable krypton atoms

We report a magneto-optical trap of metastable krypton atoms with a trap loading rate of 3×10(11) atoms/s and a trap capture efficiency of 3×10(-5). The system starts with an atomic beam of metastable krypton produced in a liquid-nitrogen cooled, radio-frequency driven discharge. The metastable beam flux emerging from the discharge is 1.5×10(14) atoms/s/sr. The flux in the forward direction is enhanced by a factor of 156 with transverse laser cooling. The atoms are then slowed inside a Zeeman slower before captured by a magneto-optic trap. The trap efficiency can be further improved, possibly to the 10(-2) level, by gas recirculation. Such an atom trap is useful in trace analysis applications where available sample size is limited.     

An atomic beam source for fast loading of a magneto-optical trap under high vacuum

We report on a directional atomic beam created using an alkali metal dispenser and a nozzle. By applying a high current (15 A) pulse to the dispenser at room temperature we can rapidly heat it to a temperature at which it starts dispensing, avoiding the need for preheating. The atomic beam produced is capable of loading 90% of a magneto-optical trap (MOT) in less than 7 s while maintaining a low vacuum pressure of <10(-11) Torr. The transverse velocity components of the atomic beam are measured to be within typical capture velocities of a rubidium MOT. Finally, we show that the atomic beam can be turned off within 1.8 s.     

Large atom number Bose-Einstein condensate of sodium

We describe the setup to create a large Bose-Einstein condensate containing more than 120 x 10(6) atoms. In the experiment a thermal beam is slowed by a Zeeman slower and captured in a dark-spot magneto-optical trap (MOT). A typical dark-spot MOT in our experiments contains 2.0 x 10(10) atoms with a temperature of 320 microK and a density of about 1.0 x 10(11) atoms/cm(3). The sample is spin polarized in a high magnetic field before the atoms are loaded in the magnetic trap. Spin polarizing in a high magnetic field results in an increase in the transfer efficiency by a factor of 2 compared to experiments without spin polarizing. In the magnetic trap the cloud is cooled to degeneracy in 50 s by evaporative cooling. To suppress the three-body losses at the end of the evaporation, the magnetic trap is decompressed in the axial direction.     

A Zeeman slower design with permanent magnets in a Halbach configuration

We describe a simple Zeeman slower design using permanent magnets. Contrary to common wire-wound setups, no electric power and water cooling are required. In addition, the whole system can be assembled and disassembled at will. The magnetic field is however transverse to the atomic motion and an extra repumper laser is necessary. A Halbach configuration of the magnets produces a high quality magnetic field and no further adjustment is needed. After optimization of the laser parameters, the apparatus produces an intense beam of slow and cold (87)Rb atoms. With typical fluxes of (1-5) × 10(10)?atoms/s at 30 m s(-1), our apparatus efficiently loads a large magneto-optical trap with more than 10(10) atoms in 1 s, which is an ideal starting point for degenerate quantum gas experiments.     

螺旋相位调制双曲余弦高斯光束的梯度力研究

光梯度力在光镊技术中起着非常重要的作用。数值模拟了螺旋相位调制双曲余弦高斯光束在焦平面上光梯度力的变化。研究结果表明:双曲余弦高斯光束的偏心参数、螺旋相位的拓扑数可以显著地调节光梯度力分布,并且会出现一些新奇的光梯度力分布,如构成圆环形光陷阱、矩形光陷阱、阵列光陷阱等;另外,对于不同数值孔径、不同拓扑数,光梯度力随双曲余弦高斯光束的偏心参数的演化规律也显著不同。     

Measurement of temperature of laser cooled atoms by one-dimensional expansion in a magneto-optical trap

We discuss a simple time of flight technique for measurement of temperature of a cold cloud in a magneto-optical trap (MOT). The technique is based on spatiotemporal fluorescence imaging of the cloud that is allowed to undergo one-dimensional expansion in the presence of the orthogonal two-dimensional configuration of laser beams by temporal modulation of a pair of counterpropagating trapping beams in the MOT. We show that, in the time scale 0< or =t<5 ms, the expansion of the cloud is ballistic and the temperature can be extracted from the time variation of the rms size of the cloud in the expansion direction. The reliability of the technique has been established by comparing the results with release and recapture method, and also by fitting them to the known temperature scaling law.     

Magneto-optical contrast in near-field optics

We propose a simple calculation of near-field magneto-optical (MO) images based on the beam propagation method. We calculate both Faraday rotation and circular dichroism contrasts of planar magnetic structures such as as-grown thin films and ion-irradiated samples. High-contrast near-field MO images are obtained, in good agreement with our experimental observations.     

Magneto-optical contrast in near-field optics

We propose a simple calculation of near-field magneto-optical (MO) images based on the beam propagation method. We calculate both Faraday rotation and circular dichroism contrasts of planar magnetic structures such as as-grown thin films and ion-irradiated samples. High-contrast near-field MO images are obtained, in good agreement with our experimental observations.     

Apparatus for vectorial Kerr confocal microscopy

We present a confocal microscopy setup that is able to record magneto-optical hysteresis cycles separating the in-plane and out-of-plane magnetization components. This apparatus is based on a modified commercial microscope, where the light beam has been deviated from the cylindrical symmetry axis of the objective lenses by inserting a translating plate in the optical path. The instrument allows for the magneto-optical imaging with a lateral resolution of 600 nm at λ = 635 nm light wavelength.     

Detection of micro gap weld using magneto-optical imaging during laser welding

Accurate seam tracking plays a critical role in acquisition of good weld. During laser butt joint welding, the laser beam focus must be controlled to follow the weld trajectory. The key problem to be solved is the automatic identification of weld position. An approach to detect the micro gap weld (gap width is less than 0.05 mm) based on magneto-optical imaging (MOI) is proposed. The laser butt joint welding of carbon steel was carried out. A magnetic excitation device was used to magnetize the weldment, and it was found that magnetic field distribution at the weld was different from other regions. The magnetized weldment was detected by using a magneto-optical sensor, and magneto-optical images of the weld were captured. By analyzing and processing weld MO images with low contrast and strong magnetic field noises, the weld center position could be detected accurately. Weld MO images at different laser welding speeds were investigated to analyze the varieties of image characteristics. Experimental results indicated that the magneto-optical imaging technique could be applied to detect the micro gap weld accurately, which provides a novel approach for automatic identification and tracking of micro gap weld during laser welding.     

A source of a high-power relativistic electron beam with high brightness

A ribbon diode of a U-2 accelerator (800 kV, ∼30 kA) intended for generating a high-intensity electron beam for heating plasma in a GOL-3 multimirror magnetic trap (Budker Institute of Nuclear Physics, Siberian Branch, Russian Academy of Sciences) is described. The parameters of the beam characterized by a high brightness (∼7 kA/(cm² sr)) in a magnetic field of ∼5 T resulting from a numerical simulation of the beam formation process are presented. The results of simulation of the beam transport and transformation of the profile of its cross section during movement of electrons in a curvilinear guiding magnetic field are presented. The calculated cross section is compared to the beam imprint on a target.     

Penning traps with unitary architecture for storage of highly charged ions

Penning traps are made extremely compact by embedding rare-earth permanent magnets in the electrode structure. Axially-oriented NdFeB magnets are used in unitary architectures that couple the electric and magnetic components into an integrated structure. We have constructed a two-magnet Penning trap with radial access to enable the use of laser or atomic beams, as well as the collection of light. An experimental apparatus equipped with ion optics is installed at the NIST electron beam ion trap (EBIT) facility, constrained to fit within 1 meter at the end of a horizontal beamline for transporting highly charged ions. Highly charged ions of neon and argon, extracted with initial energies up to 4000 eV per unit charge, are captured and stored to study the confinement properties of a one-magnet trap and a two-magnet trap. Design considerations and some test results are discussed.     

Demonstration of charge breeding in a compact room temperature electron beam ion trap

For the first time, a small room-temperature electron beam ion trap (EBIT), operated with permanent magnets, was successfully used for charge breeding experiments. The relatively low magnetic field of this EBIT does not contribute to the capture of the ions; single-charged ions are only caught by the space charge potential of the electron beam. An over-barrier injection method was used to fill the EBIT's electrostatic trap with externally produced, single-charged potassium ions. Charge states as high as K(19+) were reached after about a 3 s breeding time. The capture and breeding efficiencies up to 0.016(4)% for K(17+) have been measured.     

NIM-Sr2 锶原子光晶格钟物理系统研究

锶原子光晶格钟在基础物理研究和时间频率精密测量领域中占有重要的地位。 中国计量科学研究院在第 1 套锶原子 光晶格钟 NIM-Sr1 的基础上,开展了进一步提升光钟性能的研究,研制出了第 2 套锶原子光晶格钟 NIM-Sr2。 NIM-Sr2 的物理系 统在量子参考体系制备、钟激光探寻及系统频移评估等方面进行了重新设计。 在原子炉和磁光阱之间新增真空差分结构,使原 子炉的运行对磁光阱区域真空压力的影响降低到 1×10 -8 Pa;将塞曼减速器中的通电线圈替换为永磁铁,优化了水冷反亥姆霍 兹线圈的缠绕方式,并向外延伸塞曼减速器通光窗口,把磁光阱区域环境温度的不均匀性降低到了 0. 166 K。 系统频移评估表 明,这些物理系统的改进显著减小了 NIM-Sr2 的系统频移不确定度,达到了 7. 2×10 -18 。     

Energy-filtered electron backscatter diffraction

The electron backscatter diffraction (EBSD) analytical technique is invaluable for determining the crystallography of bulk alloys, thin films, and nanoparticles. However, our physical understanding of EBSD pattern generation is incomplete, which hinders our ability to push the limits of EBSD analysis. Here, using an energy filter with better than 10 eV resolution, we experimentally demonstrate the energy dependence of EBSD patterns from elements over a large atomic number range. We verify that low-loss electrons are the major contributors to EBSD patterns, but that there is still a diffraction contribution from electrons with only 80% of the incident beam energy. Additionally, the bands in filtered EBSD patterns have contrast that is more than twice the contrast of their unfiltered counterparts. The band contrast reaches a maximum for a cutoff energy in the filter of about 3% below the energy of the incident beam. Different mechanisms are used to explain the drop in contrast on each side of the maximum. With the cutoff set very close to the energy of the incident beam, the patterns become more blurred. We used a Monte Carlo simulation in the analysis of these experiments.     

A very low energy compact electron beam ion trap for spectroscopic research in Shanghai

In this paper, a new compact low energy electron beam ion trap, SH-PermEBIT, is reported. This electron beam ion trap (EBIT) can operate in the electron energy range of 60-5000 eV, with a current density of up to 100 A/cm(2). The low energy limit of this machine sets the record among the reported works so far. The magnetic field in the central drift tube region of this EBIT is around 0.5 T, produced by permanent magnets and soft iron. The design of this EBIT allows adjustment of the electron gun's axial position in the fringe field of the central magnetic field. This turned out to be very important for optimizing the magnetic field in the region of the electron gun and particularly important for low electron beam energy operation, since the magnetic field strength is not tunable with permanent magnets. In this work, transmission of the electron beam as well as the upper limit of the electron beam width under several conditions are measured. Spectral results from test operation of this EBIT at the electron energies of 60, 315, 2800, and 4100 eV are also reported.     

磁光阱异面空间角度测量及测量不确定度评定

随着空间几何量精密测量技术在装备制造工业的制造与装配过程中应用越来越广泛,角度计量正在从平面角度向空间角度发展。针对磁光阱的异面空间角度进行测量,使用平行平晶作为标准平面引出待测面法向量,并将其空间角度有效的划分成水平投影角和竖直投影角两个平面角度进行测量,保证了空间角度的可溯源性,得到磁光阱各待测面法向量间的空间角度偏差最大值为0.286 0 mrad;然后通过蒙特卡洛法评定该方法的测量不确定度为0.095 9 mrad;最后与三坐标测量机法比对结果中偏差最大值为0.184 2 mrad,在考虑待测面平面度指标为±0.145 4 mrad时,二者的一致性良好。目前该方法已在NIM5铯原子喷泉钟物理真空子系统的研制中进行了应用,证明了该方法能够满足测量的准确度要求。