PRODUCTION OF POLARIZED 7Li ATOMIC BEAM IN STRONG MAGNETIC FIELD BY OPTICAL PUMPING

The production of a polarized ⁷Li atomic beam in a strong magnetic field was experimentally studied by laser optical pumping of a single ground hyperfine F level. It was shown that nearly complete negative and partial positive polarizations of ⁷Li atoms could be realized under appropriate conditions by this pumping scheme, which was in agreement with the rate equation calculations. Based on the analyses of transition probabilities, the maximum polarizations for various transitions and light polarizations were given.     

Influence of atomic alignment on crossover signals in saturation spectroscopy

The crossover resonance between the atomic transitions² S _1/2(F=2)→² P _1/2(F′=1, 2), observed in the saturation spectrum of sodium, was found to be sensitive to the atomic orientation of the ground state, produced by velocity selective optical pumping. For zero magnetic field and the same linear polarization of saturating and probing beam, a negative signal was recorded for the crossover, corresponding to an increase in absorption of the probing beam. Application of a sufficiently strong magnetic field perpendicular to the polarization vector causes the destruction of the alignment, leading to a change in sign for the crossover intensity, i.e., to an enhanced transmission of the probing beam. It was shown experimentally that an increase in the atomic transit time has the same effect. Using optical pumping theory all qualitative features could be accounted for.     

PRODUCTION OF POLARIZED 7Li ATOMIC BEAM IN STRONG MAGNETIC FIELD BY OPTICAL PUMPING

The production of a polarized ⁷Li atomic beam in a strong magnetic field was experimentally studied by laser optical pumping of a single ground hyperfine F level. It was shown that nearly complete negative and partial positive polarizations of ⁷Li atoms could be realized under appropriate conditions by this pumping scheme, which was in agreement with the rate equation calculations. Based on the analyses of transition probabilities, the maximum polarizations for various transitions and light polarizations were given.     

Dual-frequency optical pumping for spin-polarizing a lithium atomic beam

A lithium-6 atomic beam is spin-polarized by means of optical pumping with a single-mode dye laser operating on the resonance transition. Simultaneous pumping of both hyperfine substates is achieved by frequency-splitting the laser light with an acousto-optic modulator. A polarization dependent signal, obtained by probing the optical activity of the beam with linearly polarized light, is utilized in a microprocessor-controlled laser stabilization scheme. The polarization is analyzed with a sextupole magnet and its overall value is 0.70 for an intensity of 1×10¹⁴ atms s⁻¹. By reversing the sense of circular polarization of the pumping light the atomic beam polarization is easily reversed in direction.     

激光减速原子束频标的建议

本文提出一个激光减速的碱金属原子束频标的方案。用共振激光束对原子束同时进行减速和选态,使原子速率降到10m/s以下,而光抽运作用使原子自动集中到基态超精细结构中具有最大磁量子数的塞曼子能级上。为避免重力场中束轨迹下垂,用偏转磁铁或多束激光使束由水平转成垂直向上,然后用级联磁共振使原子过渡到频标所需的m_F=0能级。利用原子上升和重力场中自由下落两次通过单个微波谐振腔而取得Ramsey共振信号,线宽约为¹Hz。信号用另一束激光检测。予期这种频标的稳定度和准确度可比现有束型频标提高一个数量级以上。文中详细讨论了激光减速和选态的方法,克服横向加热效应的措施,实现级联磁共振的办法,以及获得垂直束装置的设计等。     

Sensitive laserspectroscopy on ions with hyperfine split transitions

Collinear laser—fast alkaline-earth ion beam interaction can be monitored sensitively by a detection sequence consisting of optical pumping to a metastable state, state-dependent neutralization, and separate counting of ions and atoms. Deceleration of the ions prior to neutralization strongly increases the sensitivity of the method. For ions with hyperfine split transitions the sensitivity can be considerably improved by a two-step optical pumping sequence. In this contribution, the results of rate equation calculations are compared to experimental results for Ba-and Sr-beams, including a shortlived⁹⁹Sr beam of very low intensity.     

激光微波双共振导致的基态碱原子的非均衡分布

本文求得了激光微波双共振抽运碱原子束时基态原子实现最大非均衡分布的条件,这与新近的实验结果相符。分析了影响非均衡分布的机制,如相干囚禁,指出了消除其影响的途径,与双激光抽运对比,讨论了激光微波双共振抽运过程的特点。 关键词：     

Frequency-dependent optical pumping in atomic ?-systems

We consider the effects of optical pumping on the conversion of laser-frequency modulation into intensity modulation by an atomic absorption line in a vapor of alkali atoms driven in a ?-configuration. It is found that, due to optical pumping in combination with the excited-state hyperfine structure, the absorption line shape is distorted substantially as the Fourier frequency of the FM is changed. The most significant effect of the distortion is a shift of the apparent line center, which depends on how the frequency of the modulation compares with the optical pumping rate. This shift has implications for locking lasers to atomic transitions and also for FM-AM noise conversion in atomic vapors.     

Velocity selective optical pumping and repumping effects with counter and copropagating laser radiations for D<Subscript>2</Subscript> lines of rubidium

The effects of a strong control or pump laser, counter propagating or copropagating with the probe beam, on the probe absorption spectra of ⁸⁵Rb and ⁸⁷Rb-D₂ transitions have been investigated inside a room temperature Rb vapour cell. In both cases a set of strong velocity selective resonance dips are observed at different velocities. Their movements across the Doppler broadened probe absorption profile have been studied for different lock frequencies of the control laser. These spectra are modified by optical pumping effects due to the presence of another hyperfine component of the ground state. A repumping laser, from the dark hyperfine component of the ground level transfers almost 75% of the atoms from the dark state to the pump probe cycle hence reducing the optical pumping effect. A numerical simulation is done to explain the observed spectra. The effect of a control laser on the Lamb dip spectrum of the probe laser has also been investigated. The control beam is used to improve the strength of a weak hyperfine dip on the Doppler broadened probe spectrum. The strength of the hyperfine dip increases by a factor of 3.2 in presence of the control laser. The observed dips show that pump-probe spectroscopy can be used as velocity selectors of atoms.     

Eine Quelle für polarisierte Lithiumkerne

A source for nuclear polarized lithium-6 and -7 ions was built following the method of separation of the atomic hyperfine states in a strong inhomogeneous magnetic sextupole field and ionisation of the selected atoms by electron bombardment in a weak homogeneous field. The velocity distribution of the atomic beam formed by a Laval nozzle and the focussing properties of the sextupole magnet were determined using a mechanical velocity selector. After separation of the two isotopes the ion beam has an intensity of 10^?9 ampere. As no background of unpolarized lithium ions was found, a vector polarisation of (32±1)% and (24±1)% for lithium-6 and -7 and a tensor polarisation of (?32±1)% for lithium-6 can be expected.     

Parametric collective phenomena during the propagation of polychromatic laser pulses in an optically dense resonant medium without population inversion

We experimentally and theoretically study the interaction of broadband polychromatic laser pulses with an optically dense resonant extended medium without population inversion. Experimental (probe field-pumping beam) measurements of the transmission and amplification spectra were carried out in the plasma of a positive neon glow-discharge column containing a large number of metastable atoms. The strong coupling in the field-matter system and the collective behavior of the atomic system in a resonant field were attributable to a high (～10¹² cm^?3) density of atoms at the lower (metastable) level of the optical transitions under consideration and to a relatively low intensity of the interacting laser beams. We observed a broadband weakening of the probe field in the absence of pumping and its strengthening in the line wings in the presence of a strong field. We develop a theoretical model for the parametric amplification of collective interactions in dense extended media based on the solution of the semiclassical Maxwell-Bloch equations for conditions under which the pumping field does not destroy the dipole interaction between atoms through probe-field photons.     

Imaging an atomic beam using fluorescence

A fluorescence detection scheme is applied to image an atomic beam. Using two laser diodes as the sources of detection light and pumping light respectively, the fluorescence image of the atomic beam is then observed by a commercial CCD-camera, which is corresponding to the atomic state and velocity distribution. The detection scheme has a great utilization in the experiments of cold atoms and atomic optics.     

Atomic resonance behavior in laser-induced Rb atom desorption—the effect of ambient gas atoms and molecules

We report an observation that in a typical optical pumping cell containing Rb metal and 150 Torr N₂ gas, a cw laser beam of a few tens of mW and beam size 5.5 mm² can desorb Rb films on cell surfaces when the laser is tuned to the Rb D₁ line. The frequency dependence of the Rb desorption rate displays atomic resonance behavior. The desorption is suggested to be mediated by the ambient gas atoms (Rb) and molecules (N₂). The phenomenon was used to provide evidence for the existence of thin Rb films on seemingly clear cell surfaces.     

Optical pumping in an RF cooler buncher

The use of optical pumping in an RF linear Paul trap is shown to permit efficient collinear laser spectroscopy in systems where atomic ground state resonance lines are ill-suited to the fast beam technique. The case of yttrium, where laser spectroscopy has been used to study ^{86–90,92–102}Y and isomeric states of ^{87–90,93,96,97,98}Y, is highlighted.     

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     

Doppler-free spectroscopy of rubidium atoms driven by a control laser

A scheme of Doppler-free spectroscopy is experimentally demonstrated with a co-propagating control laser locking to an atomic hyperfine transition, and the differential transmission of the probe and the reference laser is detected. Crossover resonances are eliminated by selecting the class of atoms with zero velocity in the direction of beam propagation. In addition, the sub-Doppler spectrum experiences optical gain compared to the conventional saturated-absorption spectrum as a result of optical pumping.     

用脉冲取样光检测方法减小Rb87频标的光频移

本文提出了利用脉冲光抽运,脉冲取样光检测,连续微波共振的方案以减小被动式Rb⁸⁷频标中的光频移。对Rb⁸⁷基态超精细能级0—0跃迁的共振线形函数和光频移作了理论计算。实验结果定性地与理论符合,利用这种方案可望能改善被动式Rb⁸⁷频标的长期频率稳定度。 关键词：     

Radiative transfer in the lyman α spectral line with self-consistent electron velocity distribution

Radiative transfer in the Ly α spectral line in a stationary, plane-parallel plasma of constant temperature and electron density is studied using model H-atoms with only two bound levels and a continuum. For this purpose, the equation of radiative transfer is solved simultaneously with the steady-state equations of the atomic levels and the kinetic equation of the electrons. The numerical results indicate that, in hydrogen plasmas with temperatures T ? 12,000°K and electron densities n_e ? 10¹⁶cm^?3, the high-energy tail of the electron velocity distribution deviates from a Maxwell distribution, even in cases of rather large optical thicknesses and that therefore the deviations from local thermodynamic equilibrium are increased compared with estimates based on the assumption of a Maxwellian electron velocity distribution. This qualitative conclusion should hold in spite of some deficiencies of the model which are discussed.