Theoretical investigations of population trapping phenomena in atomic four-color,three-step photoionization scheme

The four-color three-step selective photoionization process of atom is very important in laser isotope separation technology.The population trapping phenomena and their influences are studied theoretically in monochromatic and non-monochromatic laser fields based on the density matrix theory in this work.Time evolutions of the photoionization properties of the four-color,three-step process are given.The population trapping effects occur intensely in monochromatic excitation,while it gradually turns weak as the laser bandwidth increases.The effects of bandwidth,Rabi frequency,time delay,and frequency detuning on the population trapping effect are investigated in monochromatic and non-monochromatic laser fields.The effects of laser process parameters and atomic parameters on the effective selective photoionization are also discussed.The ionization probability and selectivity factors,as evaluation indexes,are difficult to improve synchronously by adjusting systematic parameters.Besides,the existence of metastable state may play a negative role when its population is low enough.

In situ calibrated angle between the quantization axis and the propagating direction of the light field for trapping neutral atoms

The recently developed magic-intensity trapping technique of neutral atoms efficiently mitigates the detrimental effect of light shifts on atomic qubits and substantially enhances the coherence time. This technique relies on applying a bias magnetic field precisely parallel to the wave vector of a circularly polarized trapping laser field. However, due to the presence of the vector light shift experienced by the trapped atoms, it is challenging to precisely define a parallel magnetic field, especially at a low bias magnetic field strength, for the magic-intensity trapping of85Rb qubits. In this work, we present a method to calibrate the angle between the bias magnetic field and the trapping laser field with the compensating magnetic fields in the other two directions orthogonal to the bias magnetic field direction. Experimentally, with a constantdepth trap and a fixed bias magnetic field, we measure the respective resonant frequencies of the atomic qubits in a linearly polarized trap and a circularly polarized one via the conventional microwave Rabi spectra with different compensating magnetic fields and obtain the corresponding total magnetic fields via the respective resonant frequencies using the Breit–Rabi formula. With known total magnetic fields, the angle is a function of the other two compensating magnetic fields.Finally, the projection value of the angle on either of the directions orthogonal to the bias magnetic field direction can be reduced to 0(4)° by applying specific compensating magnetic fields. The measurement error is mainly attributed to the fluctuation of atomic temperature. Moreover, it also demonstrates that, even for a small angle, the effect is strong enough to cause large decoherence of Rabi oscillation in a magic-intensity trap. Although the compensation method demonstrated here is explored for the magic-intensity trapping technique, it can be applied to a variety of similar precision measurements with trapped neutral atoms.

BaF radical： A promising candidate for laser cooling and magneto-optical trapping

Recently, there have been great interest and advancement in the field of laser cooling and magneto-optical trapping of molecules. The rich internal structure of molecules naturally lends themselves to extensive and exciting applications. In this paper, the radical^(138)Ba^(19) F, as a promising candidate for laser cooling and magneto-optical trapping, is discussed in detail.The highly diagonal Franck–Condon factors between the X^2Σ^+_(1/2)and A^2Π_(1/2) states are first confirmed with three different methods. Afterwards, with the effective Hamiltonian approach and irreducible tensor theory, the hyperfine structure of the X^2Σ^+_(1/2)state is calculated accurately. A scheme for laser cooling is given clearly. Besides, the Zeeman effects of the upper(A^2Π_(1/2)) and lower(X^2Σ^+_(1/2)) levels are also studied, and their respective g factors are obtained under a weak magnetic field.Its large g factor of the upper state A^2Π_(1/2) is advantageous for magneto-optical trapping. Finally, by studying Stark effect of Ba F in the X^2Σ^+_(1/2), we investigate the dependence of the internal effective electric field on the applied electric field. It is suggested that such a laser-cooled Ba F is also a promising candidate for precision measurement of electron electric dipole moment.

4-7 Laser Cooling and Trapping of Rubidium Atoms

Atomic physics is developed by the realization of Magneto-Optical Trap (MOT)[1] which helps scientists achievethe miracles of Bose Einstein condensation[2], atomic frequency standard[3] and ultra-cold plasma[4]. We built arubidium MOT system and used it to cool and trap as many as 106 87Rb atoms with a density of 1010cm?3 and atemperature of 500 K.The MOT consists of three systems: the vacuum system, the laser system and the control system. The vacuumsystem is carefully designed to obtain a vacuum as high as 510?9 mbar. Rubidium atoms are evaporated intothe vacuum chamber by heating the pure rubidium metal to 40?C.

Donnan Electric Potential Dependence of Intraparticle Diffusion of Malachite Green in Single Cation Exchange Resin Particles: A Laser Trapping-Microspectroscopy Study

A laser trapping-microspectroscopy technique combined with excitation energy transfer from a fluorescent cationic dye (Rhodamine B, RB+) to a non-fluorescent cationic dye (Malachite Green, MG+) was employed to study pH effects on the diffusion coefficients of MG+ (D(MG+)) in single cation-exchange resin microparticles with the diameters of 16 μm. When RB+-pre-adsorbed resin particles were soaked in an aqueous MG+ solution, the RB+ fluorescence was quenched gradually with the soaking time. The time course of the quenching efficiency of RB+ by MG+ was then used to evaluate the D(MG+) value in the particle. The D(MG+) value increased from 1.1 × 10-11 to 4.3 × 10-11 cm2.s–1 on going the solu- tion pH value from 9 to 4. The results were explained reasonably by a Donnan electric potential model.

Microtrap on a concave grating reflector for atom trapping

We propose a novel scheme of optical confinement for atoms by using a concave grating reflector.The two-dimension grating structure with a concave surface shape exhibits strong focusing ability under radially polarized illumination.Especially,the light intensity at the focal point is about 100 times higher than that of the incident light.Such a focusing optical field reflected from the curved grating structure can provide a deep potential to trap cold atoms.We discuss the feasibility of the structure serving as an optical dipole trap.Our results are as follows.(i) Van der Waals attraction potential to the surface of the structure has a low effect on trapped atoms,(ⅱ) The maximum trapping potential is ~1.14 mK in the optical trap,which is high enough to trap cold ^(87)Rb atoms from a standard magneto-optical trap with a temperature of 120 μK,and the maximum photon scattering rate is lower than 1/s.(ⅲ) Such a microtrap array can also manipulate and control cold molecules,or microscopic particles.

Characterizing passive coherent population trapping resonance in a cesium vapor cell filled with neon buffer gas

We present a pair of phase-locked lasers with a 9.2-GHz frequency difference through the injection locking of a master laser to the RF-modulation sideband of a slave diode laser. Using this laser system, a coherent population trapping (CPT) signal with a typical linewidth of ～ 182 Hz is obtained in a cesium vapor cell filled with 30 Torr (4kPa) of neon as the buffer gas. We investigate the influence of the partial pressure of the neon buffer gas on the CPT linewidth, amplitude, and frequency shift. The results may offer some references for CPT atomic clocks and CPT atomic magnetometers.

Efficient loading of ultracold sodium atoms in an optical dipole trap from a high power fiber laser

We report on a research of the loading of ultracold sodium atoms in an optical dipole trap,generated by two beams from a high power fiber laser.The effects of optical trap light power on atomic number,temperature and phase space density are experimentally investigated.A simple theory is proposed and it is in good accordance with the experimental results of the loaded atomic numbers.In a general estimation,an optimal value for each beam with a power of 9 W from the fiber laser is achieved.Our results provide a further understanding of the loading process of optical dipole trap and laid the foundation for generation of a sodium Bose–Einstein condensation with an optical dipole trap.

Beyond Lambertian light trapping for large-area silicon solar cells:fabrication methods

Light trapping photonic crystal(PhC)patterns on the surface of Si solar cells provides a novel opportunity to approach the theoretical efficiency limit of 32.3%,for light-to-electrical power conversion with a single junction cell.This is beyond the efficiency limit implied by the Lambertian limit of ray trapping~29%.The interference and slow light effects are harnessed for collecting light even at the long wavelengths near the Si band-gap.We compare two different methods for surface patterning,that can be extended to large area surface patterning:1)laser direct write and 2)step-&-repeat 5×reduction projection lithography.Large area throughput limitations of these methods are compared with the established elec-tron beam lithography(EBL)route,which is conventionally utilised but much slower than the presented methods.Spec-tral characterisation of the PhC light trapping is compared for samples fabricated by different methods.Reflectance of Si etched via laser patterned mask was~7%at visible wavelengths and was comparable with Si patterned via EBL made mask.The later pattern showed a stronger absorbance than the Lambertian limit6.

Assessment of the Elasticity of Erythrocytes in Different Physiological Fluids by Laser Traps

In the study of the mechanical properties of the erythrocytes (red blood cells-RBCs) the blood sample is commonly diluted in fluids that do not compromise the integrity of the cells. Fetal bovine serum (FBS), newborn bovine serum (NBBS), and phosphate buffer (PBS) solution with a concentration that can provide the right osmotic pressure are fluids commonly used to dilute the blood samples in such studies. Here we have presented the effect of these fluids on the elastic properties of the RBCs that we studied using laser traps. Two laser traps are directly used to trap and deform the cell by exerting a force distributed on the entire cell. The relative changes in size of the cell are studied as a function of the applied force to investigate any effects on the mechanical deformability of RBCs when the cells are suspended in these fluids. The results have shown that the elasticity of the RBCs in the NBBS is not statistically different from the elasticity of the cells in the PBS solution;however the results for the elasticity of the cells in FBS are found to be significantly higher.

Charge trapping in surface accumulation layer of heavily doped junctionless nanowire transistors

We investigate the conductivity characteristics in the surface accumulation layer of a junctionless nanowire transistor fabricated by the femtosecond laser lithography on a heavily n-doped silicon-on-insulator wafer. The conductivity of the accumulation region is totally suppressed when the gate voltage is more positive than the flatband voltage. The extracted low field electron mobility in the accumulation layer is estimated to be 1.25 cm2·V-1·s-1. A time-dependent drain current measured at 6 K predicts the existence of a complex trap state at the Si–Si O2 interface within the bandgap. The suppressed drain current and comparable low electron mobility of the accumulation layer can be well described by the large Coulomb scattering arising from the presence of a large density of interface charged traps. The effects of charge trapping and the scattering at interface states become the main reasons for mobility reduction for electrons in the accumulation region.

Laser Controlling Wavepacket Trains of a Paul Trapped Ion

我们学习了量，单身的保罗的古典运动套住离子与一个时间周期的激光领域交往。由使用测试功能方法，我们构造量动力学的 nexact 答案与是的期望轨道描述概括挤压的协调状态相应的古典的。准确概率密度的时空进化显示出一些波浪包火车。它是由调整激光紧张和频率，我们能控制波浪包火车的中心运动的表明的经分解。Wealso 讨论象波浪包，和稳定性的回声损失的精力，宽度和高度的期望价值那样的另外的物理性质。

Experiments on trapping ytterbium atoms in optical lattices

Experiments on trapping ytterbium atoms in various optical lattices are presented.After the two-stage cooling,first in a blue magneto–optical trap and then in a green magneto–optical trap,the ultracold171Yb atoms are successfully loaded into one-,two-,and three-dimensional optical lattices operating at the Stark-free wavelength,respectively.The temperature,number,and lifetime of cold171Yb atoms in one-dimensional lattice are measured.After optimization,the one-dimensional lattice with cold171Yb atoms is used for developing an ytterbium optical clock.

输尿管镜联合封堵取石导管与N-trap拦截网治疗输尿管结石的对比研究

目的探讨输尿管上段结石的适宜处理方法,比较输尿管镜钬激光碎石联合封堵取石导管与N-Trap拦截网治疗输尿管上段结石的临床效果。方法采用整群抽样的方法并根据手术中使用辅助器械的不同分析2009年1月-2015年1月在川北医学院附属医院接受治疗的单侧输尿管结石患者223例,其中单独使用输尿管硬镜碎石54例(A组),输尿管镜联合使用封堵取石导管79例(B组),输尿管镜联合使用N-Trap拦截网90例(C组)。比较3组间一次性碎石成功率、清石率、手术时间及手术并发症发生率。结果一次性碎石成功率比较:A组37/54(68.5%),B组65/79(82.2%),C组85/90(94.4%),3组间比较差异有统计学意义(P<0.01)。清石率比较,A组为27/37(72.9%),B组为56/65(86.1%),C组为80/85(94.1%);B、C组与A组比较有统计学意义(P=0.046),表明输尿管镜联合使用结石封堵装置可提高结石清除率。手术时间:A组为(34.5±12.2)min,B组为(47.3±15.4)min,C组为(45.6±14.5)min。A组分别与B、C组比较手术时间更短,差异有统计学意义(P<0.01);B、C组比较差异无统计学意义(P=0.445)。手术并发症之间差异无统计学意义。结论对于输尿管上段结石选择单纯使用输尿管镜碎石的方法并非最佳选择。封堵取石导管与N-Trap拦截网具有不同的设计特点,但就该院临床使用的效果分析,N-Trap拦截网对结石的阻拦、提高手术成功率及清石率方面优于封堵取石导管。

基于二维磁光阱的增强型^(199)Hg冷原子团制备

在精密测量领域中,高效地制备冷原子团具有重要的意义.在光晶格钟里,缩短冷原子团的制备时间可以降低Dick噪声,从而提高光晶格钟的稳定性.本文采用二维磁光阱加推送光的构型提高了三维磁光阱在超高真空环境中的装载率,并通过压缩磁光阱技术降低了原子团温度,实现了用于^(199)Hg光晶格钟的增强型冷原子团制备.实验上通过优化三维和二维磁光阱的失谐量和磁场梯度以及推送光的失谐量和功率等参数,将三维磁光阱的^(199)Hg冷原子装载率增强了51倍,提升至3.1×10^(5)s^(–1),然后使用压缩磁光阱技术将^(199)Hg冷原子团的温度降低至45μK,低于多普勒冷却理论温度.这种基于二维磁光阱的增强型冷原子团制备可在超真空环境下实现对三维磁光阱装载率的高增益,有效地缩短了冷原子团的制备时间,同时也降低了原子团的温度,有利于提高光晶格的转移效率,为其他冷原子实验中冷汞原子团制备提供了有效方案.

激光照射对兔正畸牙齿牙周组织中TRAP表达的影响

目的 :观察氦氖激光照射对兔正畸牙齿移动牙周组织中抗酒石酸酸性磷酸酶表达的影响 ,探讨氦氖激光照射对正畸骨改建的作用。方法 :选择体质量 (1.5± 0 .2 )kg的大耳白兔 ,随机分为未加力组及加力 1、3、5、7、14、2 1d组 ,每组 5只 ,共 3 5只。 0 .0 5mol/L戊巴比妥钠经耳缘静脉麻醉 (2ml/kg) ,分别在兔左右上颌切牙和第一磨牙间放置不锈钢螺簧 ,力值为 7.84N。右侧作为实验侧 (氦氖激光照射侧 ) ,左侧作为对照侧。对实验组动物右上颌第一磨牙相应的颊部进行氦氖激光照射。标本处理后进行抗酒石酸酸性磷酸酶的染色 ,光镜下观察破骨细胞的变化。对破骨细胞中TRAP染色阳性颗粒计数并进行统计学分析。结果 :氦氖激光照射侧和对照侧相比 ,各组抗酒石酸酸性磷酸酶的表达均增高 ,3、7d组抗酒石酸酸性磷酸酶的表达有显著差异 (P <0 .0 5)。结论 :氦氖激光照射可以增强正畸牙移动过程中牙周组织内抗酒石酸酸性磷酸酶的表达 。

MALDI coupled with laser-postionization and trapped ion mobility spectrometry contribute to the enhanced detection of lipids in cancer cell spheroids

Cancer cell spheroids(CCS) are a valuable three-dimensional cell model in cancer studies because they could replicate numerous characteristics of solid tumors. Increasing researches have used matrix-assisted laser desorption/ionization mass spectrometry imaging(MALDI-MSI) to investigate the spatial distribution of endogenous compounds(e.g., lipids) in CCS. However, only limited lipid species can be detected owing to a low ion yield by using MALDI. Besides, it is still challenging to fully characterize the structural diversity of lipids due to the existence of isomeric/isobaric species. Here, we carried out the initial application of MALDI coupled with laser-postionization(MALDI-2) and trapped ion mobility spectrometry(TIMS) imaging in HCT116 colon CCS to address these challenges. We demonstrated that MALDI-2 is capable of detecting more number and classes of lipids in HCT116 colon CCS with higher signal intensities than MALDI. TIMS could successfully separate numerous isobaric/isomeric species of lipids in CCS. Interestingly, we found that some isomeric/isobaric species have totally different spatial distributions in colon CCS. Further MS/MS imaging analysis was employed to determine the compositions of fatty acid chains for isomeric species by examining disparities in signal intensities and spatial distributions of product ions. This work stresses the robust ability of TIMS and MALDI-2 imaging in analyzing endogenous lipids in CCS, which could potentially become powerful tools for future cancer studies.