激光冷却获得高亮度的亚稳态惰性气体原子束和原子阱

高强度的亚稳态惰性原子束流在原子分子物理实验研究中具有广泛的应用.使用射频电离方法和激光横向冷却技术制备了高强度的亚稳态氪原子束流,并使用数值模拟方法对横向冷却激光场中的原子径迹进行了分析.通过激光诱导荧光光谱方法测量原子束的束流特性,结果显示,横向冷却后在束流源下游230 cm处的原子束流强度达1.6atoms/(s*sr),束流强度提高了两个量级.利用这种高强度原子束流,我们成功囚禁了1.3×10¹⁰个亚稳态⁸⁴Kr原子,同时冷原子装载速率达到了3.0×10¹¹atoms/s;并利用该装置成功地实现了高亮度的亚稳态氩原子束和原子阱. 关键词： 横向冷却 原子束 原子阱 惰性气体     

激光冷却气体原子研究的起步阶段

文章记述了开展激光冷却气体原子研究的起步阶段,描述了推动文章作者从原子钟研究走向激光冷却气体原子研究的动力.在研究初期阶段,文章作者着重思考了激光冷却气体原子物理机制,如:积分球红移漫反射激光冷却气体原子的设想和利用光频移效应(交流斯塔克效应)激光冷却气体原子的物理思想.文章还描述了作者所在实验室用于激光冷却原子研究的原子束实验装置,并展示了几个物理实验结果.最后,文章还总结了经验和教训,深感起步艰辛和今日可贵,期盼光辉的未来.     

微波腔镀银实现漫反射冷却的实验研究

观测到了使用镀银微波腔产生漫反射光场冷却原子的信号,完成了微波腔与积分球一体化的最后一步。这种冷却方式结构更加简单,且没有涂料,不会对微波场场型造成影响,有利于钟信号的信噪比及对比度提高。同时测试了微波腔冷却在不同冷却光注入方案、漫反射系数及腔表面开孔尺寸下的冷却性能。结果表明端面注入冷却光是目前获得更多冷原子数目的方法,提高腔表面的漫反射系数,可以显著提高冷原子数目。为了充分利用积分球内的冷原子,采用了10mm的通光孔径,测试了不同通光孔径对冷原子信号的影响,证实了目前较大的通光孔径不会影响到冷原子数。     

40K-87Rb原子冷却的半导体激光系统

对⁴⁰K-⁸⁷Rb原子冷却的半导体激光系统提出了一种实验方案，并进行了初步实验.采用三台外腔光栅反馈半导体激光器(ECDL)、四台注入锁定从激光器和一台半导体激光放大器组成激光系统.三台ECDL通过声光调制器产生四束光，分别作为⁴⁰K和⁸⁷Rb原子的冷却光和再抽运光，四束不同频率成分的激光分别注入锁定四台从激光器，然后Rb 冷却光、K冷却光和K再抽运光再同时注入半导体激光放大器进行放大.该装置可同时产生冷却⁴⁰K和⁸⁷Rb原子的冷却光和再抽运光，结构紧凑、工作稳定. 关键词： 简并费米气体 激光器系统 外腔光栅反馈半导体激光器 半导体激光放大器     

全光学冷却与囚禁133Cs原子玻色-爱因斯坦凝聚的可能性

综述了近年来有关蒸发冷却¹³³Cs原子样品的实验进展,分析了磁囚禁¹³³Cs原子玻色爱因斯坦凝聚(BEC)的困难,并在此基础上提出了一个全光型冷却与囚禁¹³³Cs原子BEC的新方案.该方案主要由一个来自半导体激光(λ=0852μm)的倒金字塔形中空光束重力光学囚禁(pyramidal-hollow-beam gravito-optical trap,缩写为PHB GOT)和一个来自Ar⁺激光(λ=05013μm)的圆锥形中空光束重力光学囚禁(conical-hollow-beam gravito-optical trap,缩写为CHB GOT)组成.在PHB GOT中,冷原子经历了一个有效的中空光束感应的Sisyphus冷却(也即强度梯度冷却)和抽运光感应的几何冷却,原子温度将被从磁光囚禁(MOT)温度(约为60μK)冷却至几个光子反冲极限(约为2μK);而在Ar⁺中空光束囚禁(CHB GOT)中,冷原子将被Raman冷却或速度选择相干粒子数囚禁技术(velocity-selection coherent population trap,缩写为VSCPT)进一步冷却至光子反冲极限以下,并被激光频率高于原子共振频率的(也即蓝失谐的)covering光束压缩.我们就PHB冷却的动力学过程进行了Monte-Carlo模拟,并计算了Ar⁺中空光束囚禁¹³³Cs原子的光学势.研究结果表明,实现一个全光学冷却与囚禁的¹³³Cs原子BEC是可能的 关键词： 倒金字塔型中空光束重力光学囚禁 强度梯度冷却 氩离子中空光束囚禁 喇曼冷却 铯原子BEC     

铬原子束横向一维激光冷却的蒙特卡罗方法仿真

激光汇聚铬原子沉积实验中,铬原子束准直度的好坏非常重要.利用蒙特卡罗随机思想选取原子轨迹初始条件,将⁵²Cr原子以外的其他同位素、纵向速度分布和横向发散角等因素综合考虑,对铬原子束横向一维激光冷却进行了优化分析.经过与均匀取值法比较,这种方法能够更好地体现原子运动的不确定性,挑选出不参与冷却过程的同位素,使考察界面内原子束的横向位置分布更好的符合实验结果.结果显示,冷却过程中其他同位素的存在使原子束横向位置分布的中心最大值减小9.3%,半高宽增加11%,并且增加轮廓曲线的基底. 关键词： 激光冷却 蒙特卡罗方法 铬原子束     

锶原子Doppler冷却中再抽运光对原子俘获影响的理论和实验研究

本文主要研究锶原子光钟Doppler冷却过程中再抽运光对俘获冷原子参数的影响,实验上测得再抽运光光强和失谐跟所俘获原子数目的关系,并且测得了在同时注入再抽运光707 nm和679 nm后使俘获冷原子的数目提高了17倍,分析了再抽运光的失谐对俘获原子数目的影响,测得了再抽运光707 nm在失谐5 MHz的情况下俘获原子数目的波动小于3‰. 关键词： 光频标 激光冷却与俘获 原子俘获率     

极性分子的激光冷却及囚禁技术

分子由于其不同于原子的特殊性质,在原子、分子和光物理研究中有其独特的地位.冷分子研究已经开展了二三十年,取得了很多重大的进展.但是以斯塔克减速器为代表的传统冷却方案遇到瓶颈,很难进一步提高分子的相空间密度.将原子中成熟的激光冷却技术拓展到极性分子中是本领域近年来的重大突破,使得冷却和囚禁分子的范围得以大大扩展,分子的相空间密度也得以提高.本文对国内外激光冷却极性分子的最新成果进行综述,并以BaF分子为例介绍激光冷却极性分子的相关理论和技术,包括分子能级结构分析及精密光谱测量,采用缓冲气体冷却进行态制备和预冷却,以及通过冷分子束研究激光与BaF分子间的相互作用.这些为后续开展激光冷却与囚禁实验研究奠定了基础,也为开展其他新的分子冷却实验提供了参考.     

Xe-NH (X3∑-)体系的势能面和冷碰撞动力学研究

以超冷Xe原子感应冷却NH（X³∑^-）分子实验为背景,理论研究磁场中Xe和NH的冷碰撞动力学性质.通过从头算方法得到了解析表达的Xe-NH体系势能面,并在此基础上采用量子动力学计算方法,研究了磁场条件下NH低场追索态（n=0,m_j=1）的冷碰撞塞曼弛豫截面.结果表明超冷Xe原子感应冷却NH分子可能在实验上难以实施.     

超冷里德堡原子的产生以及探测

利用激光冷却与俘获技术获得冷原子,由双光子激发产生超冷里德堡原子,利用场电离法得到了里德堡原子ns和nd态的离子谱图;再将激光波长固定在6p3/2-34d态的共振跃迁线上,得到了离子和里德堡原子的TOF(Time of Flight)图,并对实验结果做了分析.     

Increasing the cold atom density in an integrating spherical cavity

A novel method of angled incidence for diffuse laser cooling of ⁸⁷Rb is presented to improve the distribution of cold atom density in an integrating sphere. The angled injection scheme could cool more atoms in the middle of the sphere compared to the previous normal injection scheme. The loading time of the cold atoms for the angled injection scheme is twice as that of the normal injection scheme. The SNR and the contrast of the detected signal would be improved in the angled injection scheme.     

Kinetic behavior of cold 87Rb atoms in integrating sphere

Kinetic behavior of cold ⁸⁷Rb atoms in integrating sphere is presented under adiabatic release. Decay time of cold atom cloud is deduced by calculation of residual cold atom number evolution under adiabatic release and agrees well with our experimental observation. Number evolutions of residual cold atoms under different kinds of acceleration have been studied in detail. Sequence laser pulse cooling is key technique for the successive operation of cold atom clock. The process of laser pulse cooling is numerically simulated and fitted with experiments, optimized distribution of cooling and dead time to get enough cold atoms is put forward to satisfy the demand of cold atom clock.     

Laser cooling of rubidium 85 atoms in integrating sphere

We cool 85Rb atoms in an integrating sphere directly from a vapor background using diffuse light generated by multiple reflections of laser beams in the inner surface of the integrating sphere. We compare and analyze the different features of cold 85Rb atoms and cold 87Rb atoms in diffuse light cooling, which are important in applying 85Rb and 87Rb isotopes in many experiments on testing fundamental physics.     

Zeeman laser cooling of <Superscript>85</Superscript>Rb atoms in transverse magnetic field

The process of Zeeman laser cooling of ⁸⁵Rb atoms in a new scheme employing a transverse magnetic field has been experimentally studied. Upon cooling, the average velocity of atoms was 12 m/s at a beam intensity of 7.2×10¹² s^?1 and an atomic density of 4.7×10¹⁰ cm^?3.     

各向同性光场对原子束的分步减速

通过理论分析计算了积分球中各向同性光场对原子产生的辐射压力,提出了一种新的激光对原子束的减速方案:将原子炉产生的热铷原子束通过五个直径为10 cm的积分球,积分球内部各向同性光场的失谐量从Δ=-70Γ依次减小到Δ=-10Γ,从而可以对原子束进行减速和冷却。通过对减速过程的数值计算结果发现,该方案可以把速度小于331 m/s的原子束减速和冷却到小于1 m/s,接近多普勒极限。     

Simultaneous magneto-optical trapping of lithium and ytterbium atoms towards production of ultracold polar molecules

We have successfully implemented the first simultaneous magneto-optical trapping (MOT) of lithium (⁶Li) and ytterbium (¹⁷⁴Yb) atoms towards production of ultracold polar molecules of LiYb. For this purpose, we developed the dual atomic oven which contains both atomic species as an atom source and successfully observed the spectra of the Li and Yb atoms in the atomic beams from the dual atomic oven. We constructed the vacuum chamber including the glass cell with the windows made of zinc selenium (ZnSe) for the CO₂ lasers, which are the useful light sources of optical trapping for evaporative and sympathetic cooling. Typical atom numbers and temperatures in the compressed MOT are 7×10³ atoms, 640 μK for ⁶Li, 7×10⁴ atoms, and 60 μK for ¹⁷⁴Yb, respectively.     

Compact magneto-optical trap for rubidium atoms

The characteristics of a magneto-optical trap (MOT) using small-diameter cooling laser beams are considered. Trapping and cooling of Rb atoms from the surrounding gas of warm atoms takes place in the trap. A compact (140 μm) and stable atomic cloud is obtained with a density of 7 × 10¹⁰ cm^?3, which is three orders of magnitude higher than the density of the surrounding gas.     

Studying the possibility of deep laser cooling of <Superscript>24</Superscript>Mg atoms in an optical lattice: Two-level quantum model

The possible deep laser cooling of ²⁴Mg atoms in a deep optical lattice in the presence of an additional pumping field resonant to the narrow 3s3s¹S₀ → 3s3p³P₁ (λ = 457 nm) optical transition is studied. Two quantum models of the laser cooling of atoms in the optical trap are compared. One is based on the direct numerical solution to the kinetic quantum equation for an atomic density matrix; it considers both optical pumping and quantum recoil effects during interaction between the atoms and field photons. The second, simplified model is based on decomposing the states of the atoms over the levels of vibration in the optical trap and analyzing the evolution of these states. The comparison allows derivation of optical field parameters (pumping field intensity and detuning) that ensure cooling of the atoms to minimal energies. The conditions for fast laser cooling in an optical trap are found.