An atom faucet

We present a simple and efficient source of slow atoms. From a background vapour loaded magneto-optical trap (MOT), a thin laser beam extracts a continuous jet of cold rubidium atoms. The jet that is typical to leaking MOT systems is created without any optical parts placed inside the vacuum chamber. We also present a simple three dimensional numerical simulation of the atomic motion in the presence of these multiple saturating laser fields combined with the inhomogeneous magnetic field of the MOT. At a pressure of P _Rb87 = 10^-8 mbar and with a moderate laser power of 10 mW per beam, we generate a flux Φ = 1.3×10⁸ atoms/s with a mean velocity of 14 m/s and a divergence of 10 mrad. Received 13 January 2001     

Rydberg hydrogen atom in the presence of uniform magnetic and quadrupolar electric fields

Laser cooling and trapping offers the possibility of confining a sample of radioactive atoms in free space. Here, we address the question of how best to take advantage of cold atom properties to perform the observation of as highly forbidden a line as the 6S-7S Cs transition for achieving, in the longer term, atomic parity violation (APV) measurements in radioactive alkali isotopes. Another point at issue is whether one might do better with stable, cold atoms than with thermal atoms. To compensate for the large drawback of the small number of atoms available in a trap, one must take advantage of their low velocity. To lengthen the time of interaction with the excitation laser, we suggest choosing a geometry where the laser beam exciting the transition is colinear to a slow, cold atomic beam, either extracted from a trap or prepared by Zeeman slowing. We also suggest a new observable physical quantity manifesting APV, which presents several advantages: specificity, efficiency of detection, possibility of direct calibration by a parity conserving quantity of a similar nature. It is well adapted to a configuration where the cold atomic beam passes through two regions of transverse, crossed electric fields, leading both to differential measurements and to strong reduction of the contributions from the M₁-Stark interference signals, potential sources of systematics in APV measurements. Our evaluation of signal-to-noise ratios shows that with available techniques, measurements of transition amplitudes, important as required tests of atomic theory, should be possible in ¹³³Cs with a statistical precision of 10^-3 and probably also in Fr isotopes for production rates of Fr atoms s^-1. For APV measurements to become realistic, some practical realization of the collimation of the atomic beam as well as multiple passages of the excitation beam matching the atomic beam looks essential.Received: 5 March 2003, Published online: 17 July 2003PACS: 32.80.Ys Weak-interaction effects in atoms - 32.70.Cs Oscillator strengths, lifetimes, transition moments - 32.80.Pj Optical cooling of atoms; trapping - 39.90.+d Other instrumentation and techniques for atomic and molecular physicsS. Sanguinetti: Also at E. Fermi Physics Dept., Pisa Univ., Pisa, Italy.     

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     

Bright thermal atomic beams by laser cooling: A 1400-fold gain in beam flux

Using a three-step transverse laser cooling scheme, a strongly diverging flow of metastable Ne(3s ³ P ₂] atoms is compressed into a well-collimated, small diameter atomic beam (e.g., 1.4 mrad HWHM divergence at 3.6 mm beam diameter) with an unmodified axial velocity distribution centered at 580 m/s. The maximum increase in beam flux 1.04 m downstream of the source is a factor 1400; the maximum increase in phase space density, i.e., brightness, is a factor 160. The laser power used is only 140 mW. The scheme is extendable to a large variety of atomic species and enables the application of bright atomic beams in many areas of physics.     

Isotope separation by laser deflection of an atomic beam

Separation of isotopes of barium has been accomplished by laser deflection of a single isotopic component of an atomic beam. With a tunable narrow linewidth dye laser, small differences in absorption frequency of different barium isotopes on the 6s^{2 1}S₀₋ 6s6p¹P₁ 5536 Å resonance were exploited to deflect atoms of a single isotopic component of an atomic beam through an angle large enough to physically separate them from the atomic beam. It is shown that the principal limitation on separation efficiency, the fraction of the desired isotopic component which can be separated, is determined by the branching ratio from the excited state into metastable states. In barium, repeated absorptions and emissions on the 5536 Å transition eventually result in decay from the 6s6p¹P₁ state to the metastable 6s5d¹D₂ state. This was observed to occur for all but 3% of the¹³⁸Ba atoms. As a result, the efficiency of separation was about 0.7 for the 8 mrad atomic beam divergence employed. (Throughput was nearly 1 mg/day. No attempt was made to maximize this value.) The isotopic purity of the separated atoms was measured to be in excess of 0.9, limited only by instrumental uncertainty. The effects of near resonant atomic scattering and excitation exchange on isotopic purity are considered. Work performed under the auspices of the U.S. Energy Research & Development Administration.     

Paramagnetic Faraday rotation with spin-polarized ytterbium atoms

We report the observation of paramagnetic Faraday rotation of spin-polarized ytterbium (Yb) atoms. As the atomic samples, we used an atomic beam, released atoms from a magneto-optical trap (MOT), and trapped atoms in a far-off-resonant trap (FORT). Since Yb is diamagnetic and includes a spin-1/2 isotope, it is an ideal sample for spin physics, such as quantum non-demolition measurement of spin (spin QND), for example. From the results of the rotation angle, we confirmed that the atoms were almost perfectly polarized. PACS 32.80.Bx; 32.80.Pj; 42.25.Lc     

Continuously transferring cold atoms in caesium double magneto-optical trap

We have established a caesium double magneto-optical trap (MOT) system for cavity-QED experiment, and demonstrated the continuous transfer of cold caesium atoms from the vapour-cell MOT with a pressure of ～ 1×10^-6 Pa to the ultra-high-vacuum (UHV) MOT with a pressure of ～ 8×10^-8 Pa via a focused continuous-wave transfer laser beam. The effect of frequency detuning as well as the intensity of the transfer beam is systematically investigated, which makes the transverse cooling adequate before the atoms leak out of the vapour-cell MOT to reduce divergence of the cold atomic beam. The typical cold atomic flux got from vapour-cell MOT is ～2×10⁷ atoms/s. About 5×10⁶ caesium atoms are recaptured in the UHV MOT.     

Stable all-optical formation of Bose–Einstein condensate using pointing-stabilized optical trapping beams

By stabilizing the beam pointing of optical trapping beams, we have succeeded in stable formation of Bose–Einstein condensate (BEC) of ⁸⁷Rb with all-optical method. The thermal effect of acousto-optic modulator (AOM) is usually one of the most serious problems to induce beam-pointing instability, especially for high power CO₂ laser. By passing the beam through AOM twice, we have improved the beam pointing from about 4.8 mrad to less than 0.4 mrad, which has been experimentally confirmed to be small enough to stably form BEC at the crossed region of CO₂ lasers as well as to perform experiments using an optical lattice which might have been affected by beam-pointing instability. PACS 32.80.Pj; 42.79.Jq; 03.75.Mn     

A high-resolution time-of-flight mass spectrometer for the detection of ultracold molecules

We have realized a high-resolution time-of-flight mass spectrometer combined with a magneto-optical trap. The spectrometer enables excellent optical access to the trapped atomic cloud using specifically devised acceleration and deflection electrodes. The ions are extracted along a laser beam axis and deflected onto an off-axis detector. The setup is applied to detect atoms and molecules photoassociated from ultracold atoms. The detection is based on resonance-enhanced multi-photon ionization. Mass resolution up to m/Δm_rms=1000 at the mass of ¹³³Cs is achieved. The performance of this spectrometer is demonstrated in the detection of photoassociated ultracold ⁷Li¹³³Cs molecules near a large signal of ¹³³Cs ions. PACS 07.75.+h; 32.80.Rm; 37.10.Gh     

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.     

First results of electron cooling experiments at LEAR

The first results are presented of electron cooling experiments in the Low-Energy Antiproton Ring (LEAR) at CERN, performed with a proton beam of about 50 and 21 MeV. The number of stored protons ranged from 10⁷ to 3 × 10⁹. Cooling times of the order 1 s and proton drag rates of up to 0.7 MeV/s were obtained. The capture of cooling electrons by protons producing hydrogen atoms was used to derive an effective electron temperature (0.25 eV). From the angular profile of the neutral hydrogen beam an upper limit of 3π mm.mrad could be deduced for the horizontal equilibrium proton-beam emittance. The lowest equilibrium momentum spread was 2 × 10⁵ (FWHM), as derived from the analysis of the longitudinal Schottky signal. This Schottky signal exhibited an unusual behaviour with beam intensity and under certain conditions showed a doublepeak structure which was associated with collective beam noise. For very cold beams transverse instabilities were observed, which resulted in a rapid spill-off of protons and a stabilization at lower intensities. The threshold of these instabilities was raised by heating the proton or the electron beam. The cooling of a bunched proton beam was investigated. The reduction of the proton momentum spread led to bunch lengths of about 2 m, containing 3 × 10⁸ protons.     

A continuous cold atomic beam from a magneto-optical trap

We have developed and characterized a new method to produce a continuous beam of cold atoms from a standard vapour-cell magneto-optical trap (MOT). The experimental apparatus is very simple. Using a single laser beam it is possible to hollow out in the source MOT a direction of unbalanced radiation pressure along which cold atoms can be accelerated out of the trap. The transverse cooling process that takes place during the extraction reduces the beam divergence. The atomic beam is used to load a magneto-optical trap operating in an ultra-high vacuum environment. At a vapour pressure of 10^-8mbar in the loading cell, we have produced a continuous flux of 7×10⁷atoms/s at the recapture cell with a mean velocity of 14 m/s. A comparison of this method with a pulsed transfer scheme is presented. Received 19 February 2001     

A cold 87Rb atomic beam

We demonstrate an experimental setup for the production of a beam source of cold ⁸⁷Rb atoms. The atoms are extracted from a trapped cold atomic cloud in an unbalanced three-dimensional magneto-optical trap. Via a radiation pressure difference generated by a specially designed leak tunnel along one trapping laser beam, the atoms are pushed out continuously with low velocities and a high flux. The most-probable velocity in the beam is varied from 9 m/s to 19 m/s by varying the detuning of the trapping laser beams in the magneto-optical trap and the flux can be tuned up to 4×10⁹ s^-1 by increasing the intensity of the trapping beams. We also present a simple model for describing the dependence of the beam performance on the magneto-optical trap trapping laser intensity and the detuning.     

Loading of a cold atomic beam into a magnetic guide

We demonstrate experimentally the continuous and pulsed loading of a slow and cold atomic beam into a magnetic guide. The slow beam is produced using a vapor loaded laser trap, which ensures two-dimensional magneto-optical trapping, as well as cooling by a moving molasses along the third direction. It provides a continuous flux larger than 10⁹ atoms/s with an adjustable mean velocity ranging from 0.3 to 3 m/s, and with longitudinal and transverse temperatures smaller than 100 μK. Up to 3×10⁸ atoms/s are injected into the magnetic guide and subsequently guided over a distance of 40 cm. Received 19 February 2002 Published online 28 June 2002     

以慢原子束方式进行原子转移的双磁光阱系统

建立了一套用于玻色-爱因斯坦凝聚实验的铷原子双磁光阱装置.从低速强源中获得慢原子束，向超高真空磁光阱进行原子转移.低速强源磁光阱与超高真空磁光阱之间可维持3个量级的压强差,超高真空磁光阱的真空度最高可达1×10^-9 Pa. 慢原子束的束流通量达1×10⁹/s. 约4×10⁸个⁸⁷Rb原子被装载到超高真空磁光阱中.还讨论了两种典型情况下磁光阱中装载的最大原子数.     

Cold atomic beam from a rubidium funnel

We report an experimental demonstration of a continuous, slow and cold beam of rubidium atoms from a two-dimensional magneto-optic trap or atomic funnel. Typically 7.3(7)×10⁸ atoms/s are ejected from the funnel with a variable velocity in the range 2–8 m/s and a temperature of 45–55 μK in the moving frame. This represents the first demonstration of sub-Doppler laser cooling in an atomic beam and temperatures as low as ≈25 μK have been observed. Received: 30 September 1999 / Published online: 5 April 2000     

Atom lithography with ytterbium beam

We successfully produced periodic ytterbium (Yb) narrow lines on a substrate using near-resonant laser light and the direct-write atom-lithography technique. The Yb atom is a promising material for nanofabrication using atom optics due to its electrical conductivity, the laser wavelength required for handling the atoms, the vapor pressure of the fabrication process, etc. The ¹⁷⁴Yb atoms collimated by Doppler cooling were channeled by the dipole force of an optical standing wave and then deposited onto a substrate. We clearly observed a grating pattern of Yb atoms fabricated on the substrate with a line separation of approximately 200 nm after examining the surface of the substrate with atomic force microscope. This is the first demonstration of nanofabrication using the atom-optical approach with Yb atoms. PACS 32.80.-t; 32.80.-Pj     

An intense, slow and cold beam of metastable Ne(3s) 3 P 2 atoms

We employ laser cooling to intensify and cool an atomic beam of metastable Ne(3 s) atoms. Using several collimators, a slower and a compressor we achieve a ²⁰Ne^* flux of 6×10 ¹⁰ atoms/s in an 0.7 mm diameter beam traveling at 100 m/s, and having longitudinal and transverse temperatures of 25 mK and 300μK, respectively. This constitutes the highest flux in a concentrated beam achieved to date with metastable rare gas atoms. We characterize the action of the various cooling stages in terms of their influence on the flux, diameter and divergence of the atomic beam. The brightness and brilliance achieved are 2.1 ×10 ²¹ s^-1m^-2sr^-1 and 5.0 ×10 ²² s^-1m^-2sr^-1, respectively, comparable to the highest values reported for alkali-metal beams. Bright beams of the ²¹Ne and ²²Ne isotopes have also been created. Received 22 June 2001     

Continuous transfer and laser guiding between two cold atom traps

We have demonstrated and modeled a simple and efficient method to transfer atoms from a first Magneto-Optical Trap (MOT) to a second one. Two independent setups, with cesium and rubidium atoms respectively, have shown that a high power and slightly diverging laser beam optimizes the transfer between the two traps when its frequency is red-detuned from the atomic transition. This pushing laser extracts a continuous beam of slow and cold atoms out of the first MOT and also provides a guiding to the second one through the dipolar force. In order to optimize the transfer efficiency, the dependence of the atomic flux on the pushing laser parameters (power, detuning, divergence and waist) is investigated. The atomic flux is found to be proportional to the first MOT loading rate. Experimentally, the transfer efficiency reaches 70%, corresponding to a transfer rate up to 2.7×10⁸ atoms/s with a final velocity of 5.5 m/s. We present a simple analysis of the atomic motion inside the pushing–guiding laser, in good agreement with the experimental data.     

An efficient pathway for Li<Superscript>6</Superscript> isotope enrichment

Separation of lithium isotopes has been achieved using two-step laser photoionization in conjunction with an atomic beam and in-house built time of flight (TOF) mass spectrometer. We present an efficient pathway for the enrichment of Li⁶ isotope by tuning the exciter laser to the 3p ² P _{1/2, 3/2} excited state of Li⁶. A concentration of up to 60% is demonstrated from a natural isotopic abundant lithium sample. In addition, the first measurement of the absolute photoionization cross-section of the 3p excited state of Li⁶ and Li⁷ are reported as 26.8±4 Mb and 25.5±3.8 Mb, respectively. PACS 32.10.Bi; 32.80.t; 32.80.Fb