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1.
刘建平  侯顺永  魏斌  印建平 《物理学报》2015,64(17):173701-173701
本文基于自行研制的第二代(180级)静电Stark减速器, 展开了对NH3的有效减速与冷却的理论研究. 首先, 计算了NH3分子在|J=1, K=1>量子态的Stark分裂, 研究了不同的同步相位角下, 减速器中NH3分子的纵向相空间稳定区域; 接着, 采用Monte-Carlo方法研究了该分子在传统工作模式下的减速效果, 并讨论了该减速模式下多个参数(包括每级损失动能、分子波包末速度和相对减速效率)与同步相位角的依赖关系, 以及减速波包末速度与减速电压的关系, 研究发现: 采用传统的Stark减速模式, 当减速电压为±13 kV、同步相位角φ0=26.08°时, 即可实现NH3从280 m/s到6.7 m/s的有效减速, 对应平动动能减少了99.9%, 其波包温度由1.34 K降至80 mK; 最后, 研究了先聚束后减速模式下NH3分子的减速效果, 以及该减速模式下减速波包末速度与同步相位角的依赖关系, 结果表明: 当减速电压为± 6.5 kV, 采用前15级电极作为聚束电极, 后165级作为减速电极时, 可将NH3分子波包的中心速度由280 m/s减至20.7 m/s, 平动动能减少了99.4%, 温度由1.34 K降至1.6 mK, 与传统减速模式相比, 冷分子波包温度降低至1/50. 由此可见, 采用180级的传统Stark减速器完全可以实现具有较低Stark势能的NH3分子的有效减速与冷却, 并获得温度约为1 mK的冷分子波包, 为进一步的实验研究提供了可靠的理论依据.  相似文献   

2.
We have calculated the Stark effect of CH3F molecules in external electrical fields,the rotational population of supersonic CH3F molecules in different quantum states,and analyse the motion of weak-field-seeking CH3F molecules in a state |J = 1,KM = 1 inside the electrical field of a Stark decelerator by using a simple analytical model.Threedimensional Monte Carlo simulation is performed to simulate the dynamical slowing process of molecules through the decelerator,and the results are compared with those obtained from the analytical model,including the phase stability,slowing efficiency as well as the translational temperature of the slowed molecular packet.Our study shows that with a modest dipole moment(~1.85 Debye) and a relatively slight molecular weight(~34.03),CH3F molecules in a state |J = 1,KM = 1 are a good candidate for slowing with electrostatic field.With high voltages of ±10 kV applied on the decelerator,molecules of 370 m/s can be brought to a standstill within 200 slowing stages.  相似文献   

3.
We produce SO2 molecules with a centre of mass velocity near zero using a Stark decelerator. Since the initial kinetic energy of the supersonic SO2 molecular beam is high, and the removed kinetic energy per stage is small, 326 deceleration stages are necessary to bring SO2 to a complete standstill, significantly more than in other experiments. We show that in such a decelerator possible loss due to coupling between the motional degrees of freedom must be considered. Experimental results are compared with 3D Monte-Carlo simulations and the quantum state selectivity of the Stark decelerator is demonstrated.  相似文献   

4.
李晓云  孙博文  许正倩  陈静  尹亚玲  印建平 《物理学报》2018,67(20):203702-203702
本文基于分子束光学Stark减速理论,提出采用调制的红失谐光晶格来减速和囚禁任意脉冲超声分子束方案,并予以理论研究.以CH4超声分子束为例,利用Monte-Carlo方法模拟了调制光晶格中的分子减速与囚禁的动力学过程,给出减速级数、同步分子初始位相角与减速效果的关系.研究结果表明:随着减速级数的增加,被减速的分子波包逐渐从原来的分子速度分布的大波包中分离开来,且减速级数越高,减速后的分子速度越小.在其他条件相同时同步分子初始位相角越大,减速波包内的分子数目越少,同时位相空间被压缩.与未调制的光晶格减速方案相比,本方案中无分子自由飞行过程,在相同的光晶格长度内完成了双倍的减速级数.当光晶格长度取3.71 mm时,模拟结果显示CH4分子从280 m/s减速至172 m/s,而未调制光晶格只能将CH4分子从280 m/s减速至232 m/s,减速效果提高了26%.本方案可以集分子的减速、囚禁于一体,是一种新型的分子光学功能器件,在冷分子光学、量子信息、冷化学等前沿研究领域中有潜在的应用.  相似文献   

5.
Stark deceleration has been utilized for slowing and trapping several species of neutral, ground-state polar molecules generated in a supersonic beam expansion. Due to the finite physical dimension of the electrode array and practical limitations of the applicable electric fields, only molecules within a specific range of velocities and positions can be efficiently slowed and trapped. These constraints result in a restricted phase space acceptance of the decelerator in directions both transverse and parallel to the molecular beam axis; hence, careful modeling is required for understanding and achieving efficient Stark decelerator operation. We present work on slowing of the hydroxyl radical (OH) elucidating the physics controlling the evolution of the molecular phase space packets both with experimental results and model calculations. From these results we deduce experimental conditions necessary for efficient operation of a Stark decelerator.  相似文献   

6.
We have decelerated a supersonic beam of 174YbF molecules using a switched sequence of electrostatic field gradients. These molecules are 7 times heavier than any previously decelerated. An alternating gradient structure allows us to decelerate and focus the molecules in their ground state. We show that the decelerator exhibits the axial and transverse stability required to bring the molecules to rest. Our work significantly extends the range of molecules amenable to this powerful method of cooling and trapping.  相似文献   

7.
We report the first experimental realization of magnetic trapping of a sample of cold radicals following multistage Zeeman deceleration of a pulsed supersonic beam. H atoms seeded in a supersonic expansion of Kr have been decelerated from an initial velocity of 520 m/s to 100 m/s in a 12-stage Zeeman decelerator and loaded into a magnetic quadrupole trap by rapidly switching the fields of the trap solenoids.  相似文献   

8.
We demonstrate a single stage optical Stark decelerator for neutral molecules which is capable of reducing the translational energy of benzene molecules within a molecular beam by 15% in a single pulsed Gaussian optical field of 15 ns duration. The change in velocity induced by the optical potential is measured by the change in the time of flight of benzene molecules ionized by a second optical field after the slowing field is turned off. A maximum reduction in the velocity of 25 m/s was measured using a single Gaussian beam with a peak intensity of 1.6 x 10(12) W/cm(2) corresponding to a maximum well depth of 253 K.  相似文献   

9.
We have designed and implemented a new Stark decelerator based on wire electrodes, which is suitable for ultrahigh vacuum applications. The 100 deceleration stages are fashioned out of 0.6 mm diameter tantalum and the array's total length is 110 mm, approximately 10 times smaller than a conventional Stark decelerator with the same number of electrode pairs. Using the wire decelerator, we have removed more than 90% of the kinetic energy from metastable CO molecules in a beam.  相似文献   

10.
The transverse motion inside a Stark decelerator plays a large role in the total efficiency of deceleration. We differentiate between two separate regimes of molecule loss during the slowing process. The first mechanism involves distributed loss due to coupling of transverse and longitudinal motion, while the second is a result of the rapid decrease of the molecular velocity within the final few stages. In this work, we describe these effects and present means for overcoming them. Solutions based on modified switching time sequences with the existing decelerator geometry lead to a large gain of stable molecules in the intermediate velocity regime, but fail to address the loss at very low final velocities. We propose a new decelerator design, the quadrupole-guiding decelerator, which eliminates distributed loss due to transverse/longitudinal couplings throughout the slowing process and also exhibits gain over normal deceleration to the lowest velocities.  相似文献   

11.
This article describes a quasi-analytic model of a linear Stark accelerator/decelerator for polar molecules in both their low- and high-field seeking states, and examines the dynamics of the acceleration/deceleration process and its phase stability. The requisite time-dependent inhomogeneous Stark fields, used in current experiments, are Fourier-analyzed and found to consist of a superposition of partial waves with well-defined phase velocities. The kinematics of the interaction of molecules with the partial waves is discussed and the notion of a phase of a molecule in a travelling field is introduced. Next, the net potential and the net force that act on the molecules are derived. A special case, the first-harmonic accelerator/decelerator, is introduced. This represents a model system many of whose properties can be obtained analytically. The first-harmonic accelerator/decelerator dynamics is presented and discussed along with that of the isomorphic biased-pendulum problem. Finally, the general properties of the velocity of the molecules in a phase-stable accelerator/decelerator are examined.Received: 11 August 2004, Published online: 23 November 2004PACS: 32.60. + i Zeeman and Stark effects - 39.10. + j Atomic and molecular beam sources and techniques - 45.50.-j Dynamics and kinematics of a particle and a system of particles - 29.17. + w Electrostatic, collective, and linear accelerators  相似文献   

12.
Deflection of a cold supersonic NO beam seeded in He has been observed when these molecules interact with both static and a resonant oscillating electric field. The NO beam splits into two beams each one deflecting about 0.5° towards the positive and negative direction of the Stark field when the employed resonant frequency between the two Stark levels of the NO molecule is 1515 kHz. This deflection angle is about four orders of magnitude higher than the value one would expect from the NO dipole moment and the employed RF field gradient. This phenomenon suggests the possibility of a significant translational motion perpendicular to the beam axis, which is induced by the resonant RF electric field on the cold and high-density supersonic beam.  相似文献   

13.
Ya-Bing Ji 《中国物理 B》2022,31(10):103201-103201
Preparation and control of cold molecules are advancing rapidly, motivated by many exciting applications ranging from tests of fundamental physics to quantum information processing. Here, we propose a trapping scheme to create high-density cold molecular samples by using a combination of electric and magnetic fields. In our theoretical analysis and numerical calculations, a typical alkaline-earth monofluoride, MgF, is used to test the feasibility of our proposal. A cold MgF molecular beam is first produced via an electrostatic Stark decelerator and then loaded into the proposed electromagnetic trap, which is composed of an anti-Helmholtz coil, an octupole, and two disk electrodes. Following that, a huge magnetic force is applied to the molecular sample at an appropriate time, which enables further compressing of the spatial distribution of the cold sample. Molecular samples with both higher number density and smaller volume are quite suitable for the laser confinement and other molecular experiments such as cold collisions in the next step.  相似文献   

14.
Here we report on the accumulation of ground-state NH molecules in a static magnetic trap. A pulsed supersonic beam of NH (a1Δ) radicals is produced and brought to a near standstill at the center of a quadrupole magnetic trap using a Stark decelerator. There, optical pumping of the metastable NH radicals to the X3Σ? ground state is performed by driving the spin-forbidden A3Π ← a1Δ transition, followed by spontaneous A → X emission. The resulting population in the various rotational levels of the ground state is monitored via laser induced fluorescence detection. A substantial fraction of the ground-state NH molecules stays confined in the several milliKelvin deep magnetic trap. The loading scheme allows one to increase the phase-space density of trapped molecules by accumulating packets from consecutive deceleration cycles in the trap. In the present experiment, accumulation of six packets is demonstrated to result in an overall increase of only slightly over a factor of two, limited by the trap-loss and reloading rates.  相似文献   

15.
The full three-dimensional velocity distributions of decelerated and accelerated particles in a Stark decelerator for Rydberg atoms and molecules have been measured. In the experiment, argon atoms in a supersonic beam are excited to low-field and high-field seeking Stark states with principal quantum number in the range n=15 to 25 and are decelerated in a 3 mm long decelerator consisting of four electrodes on which time-dependent voltages are applied. The time dependence of the resulting inhomogeneous electric field is chosen such that the decelerating force acting on the high-field seeking states is maximized at each point along the trajectories. The three-dimensional velocity distribution of the atoms before and after the deceleration is determined by measuring times of flight and two-dimensional images of the atomic cloud on the detector. Under optimal deceleration conditions, the decrease in kinetic energy in the longitudinal dimension amounts to 1.0×10-21 J and the increase in mean kinetic energy in the transverse dimensions is only 1.0×10-23 J. The corresponding temperatures of 100 mK and 300 mK in the two transverse dimensions are sufficiently low that trapping can be envisaged. The possibility of focusing a Rydberg atom beam is demonstrated experimentally.  相似文献   

16.
Deflection of a cold supersonic toluene beam seeded in He has been observed when these molecules interact with both a static and a resonant oscillating electric field. The toluene beam splits into two beams each one peaking at a deflection angle of 1 degree towards the positive and negative direction of the Stark field when the employed resonant frequency between the two Stark levels of the toluene molecule is 1411 kHz. This deflection angle is about four orders of magnitude higher than the value one would expect from the toluene dipole moment and the employed RF field gradient. Different hypothesis are suggested to explain the observed strong beam splitting including the possibility of transverse beam interferences induced by both the resonant RF field and the transverse uniform electric field. A theoretical model is presented based on molecular beam interferences induced by the resonant RF field which seems to account satisfactorily for the present observations.  相似文献   

17.
A beam of diatomic molecules scattered off a standing wave laser mode splits according to the rovibrational quantum state of the molecules. Our numerical calculation shows that single state resolution can be achieved by properly tuned, monochromatic light. The proposed scheme allows for selecting non-vibrating and non-rotating molecules from a thermal beam, implementing a laser Maxwell's demon to prepare a rovibrationally cold molecular ensemble. Received 23 August 2000 and Received in final form 17 November 2000  相似文献   

18.
We demonstrate deceleration of a beam of neutral strontium monofluoride molecules using radiative forces. Under certain conditions, the deceleration results in a substantial flux of detected molecules with velocities ?50 m/s. Simulations and other data indicate that the detection of molecules below this velocity is greatly diminished by transverse divergence from the beam. The observed slowing, from ~140 m/s, corresponds to scattering ?10(4) photons. We also observe longitudinal velocity compression under different conditions. Combined with molecular laser cooling techniques, this lays the groundwork to create slow and cold molecular beams suitable for trap loading.  相似文献   

19.
A pulsed beam of ground state OH radicals is slowed down using a Stark decelerator and is subsequently loaded into an electrostatic trap. Characterization of the molecular beam production, deceleration, and trap loading process is performed via laser induced fluorescence detection inside the quadrupole trap. Depending on the details of the trap loading sequence, typically 10(5) OH (X2Pi(3/2),J=3/2) radicals are trapped at a density of around 10(7) cm(-3) and at temperatures in the 50-500 mK range. The 1/e trap lifetime is around 1.0 s.  相似文献   

20.
An electrostatic quadrupole is used to filter slow dipolar ND3 molecules from an effusive source and to guide them into ultrahigh vacuum. The molecules in the electrostatic quadrupole experience a Stark interaction which allows filtering of small velocities in the linear and bent sections of the quadrupole. With this technique we demonstrate a flux of /s with a longitudinal temperature of a few K. The technique and the set-up are discussed in detail, and the guided gas as well as the output beam are characterized. Improvements in the set-up are highlighted, as for instance cooling of the effusive source to below 150 K.Received: 1 July 2004, Published online: 28 September 2004PACS: 33.55.Be Zeeman and Stark effects - 39.10. + j Atomic and molecular beam sources and techniques  相似文献   

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