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Physical Review A

Diagnostic technique for Zeeman-compensated atomic beam slowing: Technique and results

Peter Molenaar, P. van der Straten, H G M Heideman, H. Metcalf

Published Jan 1, 1997• 42 citations
Publisher

Abstract

We have developed a diagnostic tool for the study of Zeeman-compensated slowing of an alkali-metal atomic beam. Our time-of-flight technique measures the longitudinal velocity distribution of the slowed atoms with a resolution below the Doppler limit. Furthermore, it can map the position and velocity distribution of atoms in either ground hyperfine level inside the solenoid without any devices inside the solenoid. The technique reveals the optical pumping effects and shows in detail how the slowing within the solenoid proceeds. We find for Na that most atoms in the chosen hyperfine state are decelerated in the slowing process. The width of the velocity distribution is determined mainly by inhomogeneities in the slowing laser beam. Using the central most uniform part of an expanded laser beam, the width is reduced to 2.5 m/s, corresponding to 3.2 mK. Finally, we discuss and show a method to produce a beam with two-velocity components for the study of head-tail low-energy collisions.

DOI
10.1103/physreva.55.605

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A supersonic beam of metastable neon atoms has been decelerated by exploiting the interaction between the magnetic moment of the atoms and time-dependent inhomogeneous magnetic fields in a multistage Zeeman decelerator. Using 91 deceleration solenoids, the atoms were decelerated from an initial velocity of 580m/s to final velocities as low as 105m/s, corresponding to a removal of more than 95% of their initial kinetic energy. The phase-space distribution of the cold, decelerated atoms was characterized by time-of-flight and imaging measurements, from which a temperature of 10mK was obtained in the moving frame of the decelerated sample. In combination with particle-trajectory simulations, these measurements allowed the phase-space acceptance of the decelerator to be quantified. The degree of isotope separation that can be achieved by multistage Zeeman deceleration was also studied by performing experiments with pulse sequences generated for ²⁰Ne and ²²Ne. © 2011 American Institute of Physics.

•Dec 7, 2011•19 citations
We have developed a diagnostic tool for the study of Zeeman-compensated slowing of an alkali-metal atomic beam. Our time-of-flight technique measures the longitudinal velocity distribution of the slowed atoms with a resolution below the Doppler limit. Furthermore, it can map the position and velocity distribution of atoms in either ground hyperfine level inside the solenoid without any devices inside the solenoid. The technique reveals the optical pumping effects and shows in detail how the slowing within the solenoid proceeds. We find for Na that most atoms in the chosen hyperfine state are decelerated in the slowing process. The width of the velocity distribution is determined mainly by inhomogeneities in the slowing laser beam. Using the central most uniform part of an expanded laser beam, the width is reduced to 2.5 m/s, corresponding to 3.2 mK. Finally, we discuss and show a method to produce a beam with two-velocity components for the study of head-tail low-energy collisions.
We report on the use of a stimulated Raman transition in a slowed atomic beam to produce a narrow velocity distribution of atoms in a selected electronic state, which could be used for atomic collisions studies in the low temperature regime(1). The velocity selection is part of the deceleration process and in this sense it is unique. The atomic beam is decelerated by the radiation pressure force exerted on the atoms by a counter- propagating laser beam. The resonance condition is maintained along the deceleration path because the changing Doppler shift is compensated by Zeeman tuning the electronic sublevels(2) with a spatialy inhomogneous magnetic field. At the end of the slowing process, the initial Maxwell-Boltzman distribution is compressed to a narrow velocity distribution (Δv ~ 50 m/s), centered close to v = 0. This velocity bunching(3) increases considerably the number of atoms in each velocity class, allowing the use of velocity selection techniques as a feasible way of studying low velocity collisions.
Hydrogen atoms seeded in a supersonic expansion of Kr have been decelerated from an initial velocity of 435 m s-1 to 107 m s-1 in a multistage Zeeman decelerator. The operation of the decelerator has been fully quantified by numerical particle trajectory simulations and independent measurements of the velocity distribution by ion time-of-flight mass spectrometry following photoionization of the decelerated atoms. The velocity distributions of the decelerated atom clouds have a half-width at half-maximum of 25 ± 12 m s-1 corresponding to a temperature of ∼30 mK. These velocities and temperatures are sufficiently low that magnetic trapping of the atoms can be envisaged. © 2008 IOP Publishing Ltd.
A modular multistage Zeeman decelerator consisting of an array of solenoids has been developed to control the velocity of cold, paramagnetic atoms and molecules in supersonic beams. The translational motion these atoms and molecules was manipulated with high precision by exploiting the interaction between their magnetic moments and timedependent inhomogeneous magnetic elds. Deceleration was achieved by pulsing high currents (up to 300 A) through the solenoids of the decelerator with pulse sequences calculated to preserve the phase-space density of the atomic and molecular samples while removing a preset amount of kinetic energy. For the operation of the multistage Zeeman decelerator, solenoids and electronic units were developed to generate strong magneticeld pulses (> 2 T) with rise and fall times of only a few microseconds. An accurate three-dimensional particle-trajectory simulation program has been developed to analyze the deceleration process and optimize its e ciency. This software was thoroughly tested by systematic comparison with experimental results and enabled, in combination with measurements, the complete characterization of the spatial and velocity distributions of the decelerated and trapped atoms for di erent sets of experimental conditions. The program was essential to achieve a complete interpretation of the dynamics of the deceleration process and to devise a strategy to e ciently load the decelerated atoms and molecules into magnetic quadrupole traps. In a rst experiment, hydrogen atoms seeded in a supersonic expansion of Kr have been decelerated from an initial velocity of 435 m/s to nal velocities as low as 107 m/s in a 12-stage Zeeman decelerator. The operation of the decelerator has been analyzed by comparing the results of numerical particle-trajectory simulations with those of independent measurements of the velocity distribution by ion time-ofight mass spectrometry following photoionization of the decelerated atoms. The velocity distribution of the decelerated atom cloud was found to have a half width at half maximum of 25± 12 m/s corresponding to a temperature of ∼ 40 mK. The phase stability of the multistage-Zeeman-deceleration process has been investigated by numerical particle-trajectory simulations and experimental measurements on deuterium atoms in a 24-stage Zeeman decelerator. A one-dimensional analytical model of the phase stability in a multistage Zeeman decelerator was adapted from a one-dimensional model of phase stability in a multistage Stark decelerator and compared with the results of oneand three-dimensional particle-trajectory simulations. The comparison, which included the analysis of the e ects of nite switch-on and switch-o times of the deceleration pulses, revealed that transverse e ects in the decelerator lead to a considerable reduction of the
We have built a Zeeman-slower apparatus which produces a slow and cold cesium atomic beam. The atomic beam has a mean velocity in the range 35--120 m/s and a high atomic current of more than $2\ifmmode\times\else\texttimes\fi{}{10}^{10}$ cold atoms/s. A small longitudinal velocity spread was achieved by optimizing the termination of the slowing process. The measured value of less than 1 m/s is consistent with a numerical simulation of the slowing process. With a magnetic lens and a tilted two-dimensional optical molasses stage, the slow atomic beam is transversely compressed, collimated, and deflected. We achieve a transverse temperature below the Doppler limit. The brilliance of this beam has been determined to be $7\ifmmode\times\else\texttimes\fi{}{10}^{23}$ atoms ${\mathrm{s}}^{\ensuremath{-}1}{\mathrm{m}}^{\ensuremath{-}2}$ ${\mathrm{sr}}^{\ensuremath{-}1}.$ By optical pumping the slow atomic beam can be polarized in the outermost magnetic substates ${F=4,m}_{F}=\ifmmode\pm\else\textpm\fi{}4,$ of the cesium ground state. This brilliant beam is an ideal source for experiments in atom optics and atom lithography.
A supersonic beam of metastable neon atoms has been decelerated by exploiting the interaction between the magnetic moment of the atoms and time-dependent inhomogeneous magnetic fields in a multistage Zeeman decelerator. Using 91 deceleration solenoids, the atoms were decelerated from an initial velocity of 580m/s to final velocities as low as 105m/s, corresponding to a removal of more than 95% of their initial kinetic energy. The phase-space distribution of the cold, decelerated atoms was characterized by time-of-flight and imaging measurements, from which a temperature of 10mK was obtained in the moving frame of the decelerated sample. In combination with particle-trajectory simulations, these measurements allowed the phase-space acceptance of the decelerator to be quantified. The degree of isotope separation that can be achieved by multistage Zeeman deceleration was also studied by performing experiments with pulse sequences generated for ²⁰Ne and ²²Ne. © 2011 American Institute of Physics.