Laser guiding of cold molecules in a hollow optical fiber and continuous-wave cold molecular beam generation

A novel scheme for guiding arbitrary buffer-gas cooled neutral molecules in a hollow optical fiber(HOF) using a red-detuned HE 11 mode is proposed and analysed theoretically.We give the electromagnetic field distribution of the HE 11 mode in the HOF and calculate the optical potential of an I 2 molecule,and study the molecule guiding mechanism using a classical Monte Carlo simulation.Using a 6 kW input laser,an S-shape HOF with a 2 cm curvature radius for both bends,and an input molecular beam with a transverse temperature of 0.5 K and longitudinal temperature of 5 K,we obtain a guiding efficiency of ～0.126% for the scheme,and the transverse and longitudinal temperatures of the guided molecular beam are 1.9 mK and 0.5 K,respectively.     

第四讲 冷分子的导引、分束、反射、聚焦与囚禁等操控技术

近年来,随着冷分子制备技术的不断发展和冷分子温度的不断降低,冷分子操控技术取得了快速发展, 并日趋成熟。文章首先介绍了冷分子导引、分束、反射与聚焦等操控的技术方案、实验结果及其最新研究进展。接着重点介绍冷分子静电囚禁、磁囚禁和光学囚禁的各种方案、实验结果及最新进展。最后就冷分子操控技术的应用进行了简单的总结与展望。     

Design of a 2.5 THz submillimeter wave laser with optical pump beam guiding

A ring resonator design using the same set of mirrors for pump beam and submillimeter wave (SMMW) beam guiding is introduced. Optimal design is discussed on the example of a 2.5 THz methanol laser. It turns out that due to refocussing of the pump beam on the pinhole certain focal lengths of the focussing mirror, which mainly is responsible for the beam guiding, should be avoided. Diffraction losses and pinhole losses determine optimalg-parameters for which the pump beam guiding losses of the resonator are minimum, and optimal pump beam waist radii.The setup of an experimental laser with the optimized resonator and the experimental setup to measure laser performance are described, and results concerning laser output power, beam quality and efficiency are discussed.     

真空条件下激光诱导光纤损伤特性研究

实验研究并分析了调Q Nd:YAG 脉冲激光诱导光纤损伤特性.设计了在真空条件下全石英光纤传输1064 nm 脉冲激光实验.通过将激光注入光纤端面气压降低到10—100 Pa, 光纤端面击穿阈值提高到大气环境下的185 倍.结合光纤端面损伤形貌分析可知,光纤端面损伤主要是由于激光驻波场和烧蚀共同作用的结果,光纤端面或内部大量的缺陷降低了光纤抗激光损伤的能力.在真空条件下由于光纤端面光学击穿阈值的提高,激光诱导光纤损伤特性又表现出了另外一种损伤模式——光纤初始输入段损伤.它发生在光纤输入段附 关键词： 激光损伤 光束传输 真空 石英光纤     

Switchable vector vortex beam generation using an optical fiber

We present our experimental results on directly transforming a circular-polarized Gaussian beam into linear-polarized vector vortex beams using a two-mode fiber and demonstrate switching between the different 0th-order vector vortex modes excited and guided in the fiber. Depending on the handiness of circular-polarization of the input Gaussian light beam, its launch angle with respect to the fiber axis and by changing them appropriately it is possible to excite and switch between the different vector vortex modes and its coherent linear superposition supported by the two-mode fiber. The output optical beams due to the selectively excited vector modes in the fiber are characterized by using a rotating analyzer and a two-beam interferometer setup to study the polarization and the phase behavior of the vector vortex beam.     

Generation of CW cold CH3CN molecular beam by a bent electostatic quadrupole guiding: Monte-Carlo study

A new kind of continuous-wave (CW) cold molecular beam, methyl cyanide (CH₃CN) beam, is generated by a bent electrostatic quadrupole guiding. The Stark shift of rotational energy levels of CH₃CN molecule and its population distribution are calculated, and the dynamic processes of electrostatic guiding and energy filtering of CH₃CN molecules from a gas source with room temperature (300 K) are simulated by Monte Carlo Method. The study showed that the longitudinal and transversal temperatures of output cold CH3CN beam could be about ∼2 K and ∼ 420 mK, and the corresponding guiding efficiency was about 10⁻⁵ as the guiding voltage was 3 kV. Furthermore, the temperature of the guided molecules and its guiding efficiency can be controlled by adjusting the guiding voltages applied on electrodes.      

非线性晶体产生的空心光束中大尺寸粒子囚禁与导引

提出了一种基于非线性ZnSe晶体产生的空心光束与光泳力的大尺寸粒子二维囚禁与一维导引、三维囚禁方案.理论上分析并计算了单个非线性ZnSe晶体产生的空心光束内粒子受到的横向与纵向光泳力,纵向光泳力的大小同粒子尺寸与光束尺寸比例的四次方成正比,与空心光束功率成正比,方向与光束传播方向一致.粒子尺寸与空心光束尺寸越接近时,横向光泳力的大小越大.结果表明该光泳力可以实现对大尺寸粒子的二维囚禁,同时可对粒子进行长距离(米量级)一维定向导引;理论上分析并计算了基于双非线性ZnSe晶体产生的局域空心光束内粒子所受横向与纵向光泳力情况,光泳力与系统参数的依赖关系与单个非线性晶体产生的空心光束中的粒子受力情况类似,不同的是该条件下纵向光泳力指向光束中心.结果表明该局域空心光束可以实现大尺寸粒子的三维有效囚禁.基于非线性ZnSe晶体产生的空心光束或者局域空心光束可以作为大尺寸粒子非接触式有效操控的工具,在现代光学以及生物医学中有潜在的应用.     

A crossed focused vortex beam with application to cold molecules

We report the generation of a crossed, focused, optical vortex beam by using a pair of hybrid holograms, which combine the vortex phase and lens phase onto a spatial light modulator. We study the intensity distributions of the vortex beam in free propagation space, and the relationship of its dark spot size with the incident Gaussian beam's waist, the lens's focal length, and its orbital angular momentum. Our results show that the crossed, focused, vortex beam's dark spot size can be as small as 16.3μm and adjustable by the quantum number of the orbital angular momentum, and can be used to increase the density of trapped molecules. Furthermore, we calculate the optical potential of the blue-detuned, crossed vortex beam for MgF molecules. It is applicable to cool and trap neutral molecules by intensity-gradient-induced Sisyphus cooling, as the intensity gradient of such vortex beam is extremely high near the focal point.     

氧碘化学激光中的增益光导效应

 发现和分析了氧碘化学激光中的增益光导效应。碘注入的不均匀等导致增益在该方向的不均匀。采用预混模型和Fabry Perot腔模型，推导了碘不均匀分布情况下的单重态氧的产额和激光束横向分布的解析表达式。计算结果表明，由于增益光导效应，引起激光横向分布的变化，可导致光束在碘注入方向的倾斜，以及输出功率的下降。     

Deceleration of a continuous-wave （CW） molecular beam with a single quasi-CW semi-Gaussian laser beam

We propose a promising scheme to decelerate a CW molecular beam by using a red-detuned quasi-cw semi-Gaussian laser beam （SGB）. We study the dynamical process of the deceleration for a CW deuterated ammonia （ND3） molecular beam by Monte-Carlo simulation method. Our study shows that we can obtain a ND3 molecular beam with a relative average kinetic energy loss of about 10% and a relative output molecular number of more than 90% by using a single quasi-cw SGB with a power of 1.5kW and a maximum optical well depth of 7.33mK.     

光子晶体光纤纤芯整形获得中空模式输出

实验研究了高非线性光子晶体光纤中模式控制的非线性过程,利用激发出高阶模式获得上转换到可见光波段的色散波.通过控制输入飞秒激光的偏振方向,获得了两组相互正交的高阶模式的非线性输出.进一步在光子晶体光纤空气孔包层中注入蜡修整纤芯结构,使得正交模式的有效模折射率差降低,从而形成简并的模式,并通过叠加简并模式获得了中空模场的输出. 关键词： 光子晶体光纤 飞秒激光 频率变换 中空模式     

OH分子束产生及其相关特性研究

以Ar为载气,采用直流脉冲放电,产生了OH超声分子束,研究了实验参量对实验结果的影响,并建立了理论模型,较好地解释了实验现象.对OH(A2Σ-X2Π)(0,0)带发射光谱强度分布进行了测量与分析,获得实验条件下的振动温度与转动温度分别为4170 K与3075 K.     

氧碘化学激光中的增益光导效应

发现和分析了氧碘化学激光中的增益光导效应。碘注入的不均匀等导致增益在该方向的不均匀。采用预混模型和Fabry Perot腔模型,推导了碘不均匀分布情况下的单重态氧的产额和激光束横向分布的解析表达式。计算结果表明,由于增益光导效应,引起激光横向分布的变化,可导致光束在碘注入方向的倾斜,以及输出功率的下降。     

Electrostatic surface guiding of cold polar molecules with a single charged wire

This paper proposes a scheme to guide cold polar molecules by using a single charged wire half embanked in an insulating substrate and a homogeneous bias electric field, which is generated by a plate capacitor composed of two infinite parallel metal plates. The spatial distributions of the electrostatic field produced by the combination of the charged wire and the plate capacitor and the corresponding Stark potentials (including dipole forces) for metastable CO molecules are calculated, the relationships between the electric field and the parameters of our charged-wire layout are analysed. It also studies the influences of the insulator on the electric field distribution and the discharge effect. This study shows that the proposed scheme can be used to guide cold polar molecules in the weak-field -- seeking states, and to form various molecule-optical elements, such as molecular funnel, molecular beam-splitters and molecule interferometer, even to construct a variety of integrated molecule-optical elements and their molecule chips.     

Second harmonic generation of high power Cosh-Gaussian beam in cold collisionless plasma

The purpose of this study is to explore the second harmonic generation (SHG) of a high power Cosh-Gaussian beam in cold collisionless plasma. The ponderomotive force causes carrier redistribution from high field to low field region in presence of a Cosh-Gaussian beam thereby producing density gradients in the transverse direction. The density gradients so produced the results in electron plasma wave (EPW) generation at the frequency of the input beam. The EPW interacts with the input beam resulting in the production of 2nd harmonics. WKB and paraxial approximations are employed for obtaining the 2nd order differential equation describing the behavior of the beam's spot size against normalized distance. The impact of well-established laser-plasma parameters on the behavior of the beam's spot size and SHG yield are also analyzed. The focusing behavior of the beam and SHG yield is enhanced with an increase in the density of plasma, the radius of the beam and the decentred parameter, and with a decrease in the intensity of the beam. The results of the current problem are really helpful for complete information of laser-plasma interaction physics.     

Demonstration of a cold atom beam splitter on atom chip

We report an experimental demonstration of a new scheme to split cold atoms on an atom chip. The atom chip consists of a U-wire and a Z-wire. The cold atom cloud is initially loaded and prepared in the Z-trap, which is split into two separate parts by switching on the current of the U-wire. The two separate atom clouds have a distance more than one millimeter apart from each other and show almost symmetrical profiles, corresponding to about a 50/50 splitting ratio.     

Propagation of anomalous hollow beam through a misaligned first-order optical system

In this paper, we consider the propagation of an anomalous hollow beam passing through the first-order ABCD optical system. Based on the generalized diffraction integrals, a general propagating formula of anomalous hollow beam is derived. Based on the derived formula, the propagation properties of anomalous hollow beam through the misaligned optical system are numerically illustrated. From the numerical results we can get that when an anomalous hollow beam propagates through a misaligned optical system, the shape of the output beam changes as the propagation distance increases, and the center of the output beam is deviated from the optical axis. The position of the output beam is effected by the misaligned parameters, and can be controlled by adjusting them. This method provides a convenient tool for studying the propagation and transformation of an anomalous hollow beam through the misaligned optical system.     

宽束冷阴极离子源分时中和技术的研究

离子束辅助镀膜沉积过程中,绝缘薄膜表面的电荷积累效应严重影响了薄膜质量。通过对宽束冷阴极离子源引出栅部分的改进,采用分时引出电子和离子方法,使正负电荷中和,以消除薄膜表面的放电现象,并对引出电子束的束流密度、能量、发射角等参数进行了测试。实验结果表明：在引出电压为600V时,电子的平均能量为100eV左右;引出电子束的发射角可以达到±40°,在±15°范围内的束流密度波动小于±5%。引出电子的束流密度较同参数下的离子束流密度小,通过调节脉冲电源的占空比,可达到很好的中和效果。     

Nanoscale guiding for cold atoms based on surface plasmons along the tips of metallic wedges

We propose a novel scheme to guide neutral cold atoms in a nanoscale region based on surface plasmons (SPs) of one pair and two pairs of tips of metallic wedges with locally enhanced light intensity and sub-optical wavelength resolution. We analyze the near-field intensity distribution of the tip of the metallic wedge by the FDTD method, and study the total intensity as well as the total potential of optical potentials and van der Waals potentials for 87 Rb atoms in the light field of one pair and two pairs of tips of metallic wedges. It shows that the total potentials of one pair and two pairs of tips of metallic wedges can generate a gravito-optical trap and a dark closed trap for nanoscale guiding of neutral cold atoms. Guided atoms can be cooled with efficient intensity-gradient Sisyphus cooling by blue-detuned light field. This provides an important step towards the generation of hybrid systems consisting of isolated atoms and solid devices.     

囚禁状态冷分子离子制备及应用

冷分子离子,尤其是在离子阱中空间囚禁起来的冷分子离子具有空间定域、可长时间存储以及和与环境分离的特性。这些特性使得空间囚禁的冷分子离子在分子光谱精密测量、探测分子离子与中性分子之间的碰撞反应等方面越来越受到人们的重视,并在最近几年得到了快速的发展。文章介绍了冷分子离子的产生方法,及其近几年在精密测量和低温下的碰撞反应等研究领域取得的主要研究成果。