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 HE₁₁ mode is proposed and analysed theoretically. We give the electromagnetic field distribution of the HE₁₁ mode in the HOF and calculate the optical potential of an I₂ 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.     

Generation of CW cold CHCN 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.     

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.     

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.      

Atom waveguide and 1D optical lattice using a two-color evanescent light field around an optical micro/nano-fiber

We propose a two-color scheme of atom waveguides and one-dimensional （1D） optical lattices using evanescent wave fields of different transverse modes around an optical micro/nano-fiber. The atom guide potential can be produced when the optical fiber carries a red-detuned light with TE01 mode and a blue-detuned light with HEll mode, and the 1D optical lattice potential can be produced when the red-detuned light is transformed to the superposition of the TE01 mode and HE11 mode. The two trapping potentials can be transformed to each other for accurately controlling mode transformation for the red-detuned light. This might provide a new approach to realize flexible transition between the guiding and trapping states of atoms.     

Electrostatic guiding of cold polar molecules on a chip

We propose a novel scheme to guide cold polar molecules on the surface of an insulating substrate (i.e. a chip) using an electrostatic field generated by the combination of a pair of parallel charged wires and a grounded metal plate. The spatial distributions of the electric fields from the above charged-wire layout and their Stark potentials for cold CO molecules and dipole forces are calculated, and the relationships between the electric field and the geometric parameters of our charged-wire system are analyzed. Our study shows that our charged-wire scheme can be used to guide cold polar molecules in the weak-field-seeking state, and to construct various molecular optical elements, such as a molecular funnel, a molecular beam splitter and a molecular interferometer and so on, to form various integrated molecular optical elements and their molecular chips, and even to generate a continuous wave (CW) cold molecular beam by using a low-pass energy filter based on bent two-wire guiding.     

Electrostatic surface guiding for cold polar molecules: experimental demonstration

We demonstrate an electrostatic surface guiding for cold polar molecules over a long distance of 44.5 cm, 0.85 mm above a dielectric substrate, and measure the transverse distribution of the guided supersonic D2O/CH3Br beam and its longitudinal velocity one. Also, we study the dependence of the relative guiding efficiency and the transverse temperature of the guided molecular beam on the guiding voltage, and show that the absolute guiding efficiencies from the Monte Carlo simulation and theoretical calculation multiplied by 3 are about equal to the measured relative one.     

空心光纤中LP01模的场分布

本文用弱导光纤近似分析了空心光纤LP01模的场分布,得出了色散方程,并进行了数值计算.     

Long wavelength vertical transition quantum cascade lasers operating CW at 110 K

The continuous wave (cw) operation of a quantum cascade laser at wavelengths ∼8 μm is reported. The structures, grown by molecular beam epitaxy in the AlInAs/GaInAs material system, are based on a vertical intersubband transition scheme and use a plasmon-enhanced waveguide geometry to reduce the losses and increase the confinement factor. The single mode optical power from one facet is 2 mW at a maximum operating temperature of 110 K. In pulsed operation the highest temperature is 210 K and the threshold shows a weak temperature dependence typical of this class of lasers, with aT_o=110 K.     

采用Damman光栅实现冷原子或冷分子囚禁的光阱阵列

提出了一种采用Damman光栅和球面透镜组合光学系统产生二维光阱阵列的新方案. 在使用红失谐高斯激光束照射的条件下，推导了计算光阱阵列的周期、光强分布、光强梯度和光阱几何参数的经验公式，讨论了此光阱阵列的特点以及在原子光学和分子光学中的应用. 研究结果表明，这种光阱阵列方案比已有的光阱阵列方案更为简单可行、操作方便，非常适用于冷原子或冷分子的阵列囚禁，以及制备新颖的光学晶格. 关键词： 冷原子或冷分子 光阱阵列 Damman光栅 光偶极势     

Experimental Study on Electrostatic with Two Guiding of Supersonic D20 Molecular Beam Charged Wires

We demonstrate the guiding of a supersonic heavy-water （D2O） molecular beam using a hollow electrostatic field generated by the combination of two parallel charged-wires and two grounded metal-plates, and report some new and preliminary experimental results. In the experiment, we detect the guiding signals by using the method of time-of-flight mass spectrum and study the dependence of the relative transmission of the beam guide on the guiding voltage. Our study shows that the relative transmission of the beam guide is increased linearly with increasing guiding voltage Vguid, and the number of the guided D20 molecules is at least increased by 89.4% when the guiding voltage is ＋20.0k V. Finally, some potential applications of our guiding scheme in the molecule optics are briefly discussed.     

Theoretical Analysis and Experimental Study on Generation of a Dark Hollow Beam by a Micron-sized Hollow Optical Fiber

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向列相液晶中光致非线性效应的研究

分析了向列相液晶中的光致非线性效应.在此基础上,基于液晶显示器工作原理设计了光控光器件.提出简化模型并利用琼斯矩阵给出光在该模型中的传输理论;引入斜入射的控制光束代替外加电压来调控液晶盒中分子的排列,实现对出射信号光的位相和光强的光-光调控;利用5CB液晶的温度特性分析环境温度对光-光调控的影响.理论分析表明:出射光位...     

Longitudinal focusing and cooling of a molecular beam

A neutral polar molecule experiences a force in an inhomogeneous electric field. This electric field can be designed such that a beam of polar molecules is exposed to a harmonic potential in the forward direction. In this potential the longitudinal phase-space distribution of the ensemble of molecules is rotated uniformly. This property is used to longitudinally focus a pulsed beam of ammonia molecules and to produce a beam with a longitudinal velocity spread of 0.76 m/s, corresponding to a temperature of 250 mu K.     

Accurate determination of the relative concentrations of ammonia isotopologues in a cold,electrostatically guided molecular beam

Buffer-gas cooling and electrostatic velocity selection techniques are combined in this work to produce a continuous molecular beam with rotational and translational temperatures comparable to those in the interstellar medium (ISM). A number of different mixtures of the isotopologues of ammonia (ND₃, ND₂H, NH₂D and NH₃) in varying ratios are used as the source gas, and the molecular beam emanating from the quadrupole guide velocity selector is characterised using mass spectrometry and Monte Carlo trajectory simulations. The guiding of the mixed isotopologues ND₂H and NH₂D is demonstrated for the first time. This approach establishes both the relative concentrations of each species in the beam and the internal rotational state distributions after buffer-gas cooling and guiding. Such information is essential for experiments in which the beam is used in reaction rate measurements (e.g., for ion–molecule reactions) and facilitates the study of reactions relevant to deuterium fractionation in the ISM, such as the competition between H and D transfer with mixed species including ND₂H and NH₂D.     

9.4 GHz过模光滑壁TE11HE11模式变换器设计

采用半径微扰的光滑壁圆波导产生HE11模,避免了常规微波领域中采用的波纹渐变转换器在高功率微波领域应用时易发生齿间打火的不足。采用基于模式耦合理论的迭代综合方法优化了不规则的半径渐变轮廓,使输出产生组成HE11模的混合模式。并通过全电磁波仿真软件进行了对比, 输出波束标量高斯含量在9.1~9.7 GHz范围内均高于99.5%,功率容量4.9 GW。     

亚微米局域空心光束的产生及其在单原子囚禁与冷却中的应用理论研究

提出了一种采用单模光纤、环形二元相位板和微透镜组成的光束整形系统产生亚微米局域空心光束的方案. 根据瑞利-索莫菲衍射积分公式, 数值计算了微透镜焦平面附近的场分布, 详细研究了空心光束的暗斑尺寸与单模光纤模场半径和微透镜焦距的关系. 数值计算结果表明: 在微透镜焦平面附近光场分布近似对称, 在焦点处场强近似为零, 周围场强逐渐增大, 形成半径约为0.4 μm的三维封闭的球形空心光场区域, 即亚微米局域空心光束. 当局域空心光束为蓝失谐时, 光场中的原子将被囚禁在光场最弱处. 若加上抽运光, 原子将受到蓝失谐局域空心光束与抽运光共同激发的强度梯度Sisyphus冷却. 本文利用该方案产生的亚微米局域空心光束构建单原子的囚禁与冷却器件, 并以单个⁸⁷Rb原子为例, 利用Mont-Carlo方法研究亚微米局域空心光束中单原子囚禁与强度梯度冷却的动力学过程, 结果表明利用该器件可以获得温度在5.8 μK量级的超冷单原子.     

一种实现冷分子囚禁的可控制静电双阱方案

提出了采用双环形载荷导线和两透明电极系统实现冷分子静电囚禁的可控制静电双阱的新方案,计算了带电圆导线和带电板所产生的静电场分布,从几个方面分析了这个囚禁方案的优点. 提出了一种有效的冷分子装载方法,并研究了双阱到单阱的演化过程. 研究表明,该可控制静电双阱方案不仅方便装载与操控弱场搜寻态的极性冷分子,而且在分子物质波的干涉、纠缠、冷碰撞,甚至进行双阱分子BEC研究等分子光学领域中有着广阔的应用前景. 关键词： 极性冷分子 静电囚禁 可控制静电双阱 分子光学     

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.     

Frequency-domain modal delay measurement for higher-order mode fiber based on stretched pulse interference

We propose and demonstrate a novel modal delay measurement technique for a higher-order mode fiber (HOF) based on optical frequency-domain reflectometry (OFDR) using an extremely simple, entirely passive, and ultrafast wavelength sweeping mechanism, namely, dispersion-induced optical pulse stretching. We obtained a high temporal resolution of approximately 1.12 ps, which was sufficient for discerning the four excited modes in an HOF with a length of only approximately 5 m. The results from our measurements were very consistent with those obtained by using a traditional time-domain measurement method and a conventional OFDR measurement based on a tunable CW laser. Our proposed technique can be also easily adapted to perform conventional time-domain modal delay measurements for very long HOFs.