Collimation of an atomic beam using retarded dipole force

We report the experimental study of collimation of an atomic beam using retarded dipole force. The transverse velocity of the atomic beam has been reduced from 50 to 15 cm/s, which corresponds to decrease in transverse efficient temperature from 350 to 33 μK. It has been found that a good collimation of the atomic beam can not be obtained at small detuning Δ, where Δγ (γ is the natural line width of the atom), because the retarded dipole force changes its sign in a small region of atomic velocities.     

The solution of a wedge disclination dipole interacting with an annular inclusion and the force acting on the disclination dipole

The interaction between a wedge disclination dipole and an elastic annular inclusion is investigated. Utilizing the Muskhelishvili complex variable method, the explicit series form solutions of the complex potentials in the matrix and the inclusion region are derived. The image force acting on the disclination dipole centre is also calculated. The influence of the location of the disclination dipole and the thickness of the annular inclusion as well as the elastic dissimilarity of materials upon the equilibrium position of the disclination dipole is discussed in detail. The results show that a stable equilibrium point of the disclination dipole near the inclusion is found for certain combinations of material constant. Moreover, the force on the disclination dipole is strongly affected by the position of the disclination dipole and the thickness of annular inclusion. The repulsion force increases （or the attraction force reduces） with the increase of the thickness of the annular inclusion. An appropriate critical value of the thickness of the annular inclusion may be found to change the direction of the force on the disclination dipole. The present solutions include previous results as special eases.     

Cavity-enhanced toroidal dipole force traps for dark-field seeking species

Dipole force traps for dark-field seeking states of atoms and molecules require regions of low intensity that are completely surrounded by a brighter optical field. Confocal cavities allow the resonant enhancement of these interesting transverse mode superpositions, and put deep far-off-resonance traps within reach of low-power diode lasers. In this paper, we show how an array of dark-field rings may be created simply using a single Gaussian beam. Such a geometry lends itself to the study of toroidal Bose–Einstein condensates.     

飞秒激光场中原子所受光学偶极力研究

通过求解全波矢布洛赫方程研究了两能级原子与飞秒超快激光脉冲的相互作用过程,计算了不同拉比频率取值下原子所受光学偶极力和粒子数布居随时间的演化情况,分析了光场失谐量对光学势分布情况的影响.研究发现:由飞秒激光场产生的横向光力的时间平均值并不等于零,而是随着拉比频率的增加呈现振荡的增大趋势;纵向光力的时间平均作用也并非是拉比频率的单调函数,而是随着拉比频率的增加呈现周期性的振荡分布特性;光学势的分布对光场的失谐量具有明显的依赖性,随着失谐量的变化,光学势的性质也随之发生了改变.     

Internal laser-induced dipole force at work in C60 molecule

We show how the many electron response of a complex molecule to an intense laser field can be incorporated with the single active electron picture. This enables us to introduce an "over-the-barrier" model for Cz+60 ionization, valid for long wavelength light. Using infrared radiation, we confirm the model and also produce stable, highly charged C60 reaching C12+60, the highest charge state ever observed. At high intensities and high charge states the internal laser-induced dipole force and rapid charging lead to stress on the molecule. The interplay between the forces provides control and suggest strategies for reaching even higher charge states.     

High-density trapping of cold ytterbium atoms by an optical dipole force

We have succeeded in trapping a high density of rare-earth atom of ytterbium (Yb) in a crossed far-off resonance trap. The peak density reaches more than 10(14) cm(-3). With a new method of a delayed crossed far-off resonance trap, we have elucidated that the atoms became concentrated into the cross region by atom-atom collisions. We trap fermionic Yb atoms in the same way as bosonic ones.     

Rectification of the dipole force in a monochromatic field created by elliptically polarized waves

The rectification of the force of induced light pressure in laser fields formed by elliptically polarized running waves in zero magnetic field is considered. Explicit analytic expressions for the induced and spontaneous forces of light pressure exerted on a stationary atom are obtained for two classes of closed optical transitions: J _g=J→J _e=J+1 and J _g=J→J _e=J (J is half-integral), where J _g and J _e are the total angular momenta of the ground and excited energy levels. It is shown that the ellipticity of waves is the necessary condition for the emergence of the rectification of the induced force in a monochromatic field. The optimal parameters of the field and the maximum rectification coefficient are calculated for a number of optical transitions. The dependence of the rectified force on the velocity is investigated analytically and numerically for the simplest 1/2→1/2 transition.     

A traveling-wave stripline dipole antenna on a substrate lens at terahertz frequency

In this paper, a study of a stripline dipole antenna on a substrate lens used as a photoconductive detector in a terahertz system is presented. The traveling-wave behavior of the stripline dipole and the influence of the substrate lens are investigated over a broad frequency range up to 5.0 THz. The numerical results show that the lens shape represented by the ratio of the extension length to the lens radius plays an important role in maximizing the antenna gain and radiation spectral bandwidth. The gain response exhibited an increased level of sensitivity to the lens shape as the lens size increased, and this is particularly important in optimizing large substrate lenses. Improvements in the gain level over the entire frequency range of interest were observed as the lens diameter increased. This study provides helpful guidelines in choosing and optimizing a substrate lens designed for a terahertz photoconductive antenna, which is particularly useful for specific applications requiring a miniaturized photoconductive antenna design.     

电偶极子和磁偶极子在外场中受力和力矩公式的一种简明推导

利用电偶极子的电荷密度和磁偶极子的电流密度的表达式,并借助δ函数导出了电偶极子和磁偶极子在外场中所受的力和力矩公式.     

Ignition of a nonresonant microwave discharge

The ignition of a 2.45 GHz microwave plasma source by a temporary local magnetic field quenching to ECR value has been studied. The source operates at high magnetic fields (ω_ce > ω) and at overcritical electron densities (ω_pe > ω). This ignition method appears to be attractive also for microwave plasma sources in toroidal devices.     

Molecular force field ellipses of Boron trihalides

The Green's function analysis and the comprehensive expressions for the potential constants for planar XY₃-type molecules given by earlier authors have been made use of in studying the elliptical behaviour of the symmetry force fields with the mixing parameter for Boron trihalides and the force constants derived from the ellipses are discussed.     

Analysis of the healthy rabbit lens surface using MAC Mode atomic force microscopy

In this investigation healthy rabbit crystalline lenses were characterized by atomic force microscopy (AFM). The lenses were cut in slices with thickness with 1mm and thus, put after cortex distinct regions of nucleus and cortex for AFM examination. AFM analysis were carried out using a PicoSPM I operating in Mac Mode. We obtained topographic images of rabbit lenses and a quantitative analysis of the width and height of fibers for nucleus and cortex regions. The longitudinal section analysis of fibers in the nucleus region indicated structures with an average width of 200nm and average height of 200nm. The intershells distance was determined as 4microm. Fiber cell cross-section dimensions, longitudinal and transverse widths, could be estimated in these regions from the AFM images. Structures with average widths as small as 1.0microm are observed in the nucleus; the intershell distance is 4.0microm. In cortical regions, hexagonal structures with average longitudinal and transverse widths of 5.0mum and 3.0mum, respectively, were identified. Three-dimensional images of tissue sections with resolution on a nanometer scale were obtained. The potential of AFM analysis for characterizing healthy and pathologic lens tissues is discussed.     

聚焦透镜的像散对光阱力的影响

根据里查德-沃耳夫矢量积分公式,研究了径向偏振光通过具有像散的大数值孔径物镜后在焦点附近的光阱力。着重研究像散对轴向和横向光阱力的影响。研究结果表明,像散的存在导致了光阱力的势垒减弱,光阱中心的偏移,甚至是改变了有效捕捉区域,这将严重影响了光镊的轴向和横向对粒子的捕捉。通过对改变数值孔径的大小和孔径与光腰的比值,以及对不同大小的粒子捕捉效果的对比,可以改变像散对粒子捕捉影响的程度,从而改善像散对光阱力的影响,这对于光镊等精密仪器的操作是十分必要的。     

Sensing dipole fields at atomic steps with combined scanning tunneling and force microscopy

The electric field of dipoles localized at the atomic steps of metal surfaces due to the Smoluchowski effect were measured from the electrostatic force exerted on the biased tip of a scanning tunneling microscope. By varying the tip-sample bias the contribution of the step dipole was separated from changes in the force due to van der Waals and polarization forces. Combined with electrostatic calculations, the method was used to determine the local dipole moment in steps of different heights on Au(111) and on the twofold surface of an Al-Ni-Co decagonal quasicrystal.     

余弦平方高斯光束通过无光栏透镜的梯度力

基于Collins公式推导了余弦平方高斯光束通过无光栏透镜光学系统聚焦后的光强分布及梯度力,采用数值模拟分析梯度力分布及光阱的数量、位置及尺度随光束参数、光束入射距离及系统菲涅耳数的变化。结果表明:光束相关参数b越大光阱的数量越多,光阱的位置随光束入射距离而改变,大小随系统菲涅耳数的增加而减小,但不影响其位置。     

The microwave spectrum,force field and dipole moment of CF2

Measurements of the microwave spectrum of CF₂ have been extended to include transitions up to J = 40. Using these extended measurements, a centrifugal distortion analysis has been performed and from the distortion constants, the force field, infrared spectrum, average structure, Coriolis coupling constants, and inertial defect have been calculated. The original assignment of the infrared spectrum has been confirmed. An improved value for the dipole moment, 0.469 ± 0.026 D, has been obtained.     

Characteristics of microwave resonators with nonresonant power leakage

We derive the formulas for the characteristics of microwave measuring resonators with nonresonant leakage of the signal from the input to the output of the resonator. It is shown that such a leakage can significantly distort the shape of the resonance curve and lead to errors when determining the Q-factor and the resonant frequency. The accuracy of approximating the experimental resonance curve of a resonator with nonresonant power leakage by two functions is compared in the cases of the classical resonance function and the generalized function allowing for the absolute value and phase of the direct-leakage signal. The use of the generalized resonance function makes it possible to reduce the approximation error and obtain a high accuracy of the Q-factor and the resonant frequency from the distorted resonance curve with nonresonant power leakage.