Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Journal of the Optical Society of America B

Magneto-optical trapping and its application to helium metastables

Harold J. Metcalf

Published Nov 1, 1989• 49 citations
Publisher

Abstract

A quantitative discussion of several interesting and attractive properties of magneto-optical traps is presented. Calculations are given for the trap depth, sample size, and intrinsic cooling capability of this especially simple example of a radiative force trap. The discussion is directed toward the cooling and confinement of metastable 23S neutral helium, and a new loading procedure suitable for this atom is proposed. It is planned to operate the trap and to cool atoms in it with 1.08-μm light from solid-state, single-mode lasers pumped by efficient diode lasers. Because of the dissipative nature of the radiative force, a trapped sample of atoms may be magnetically compressed without increasing its millikelvin optical temperature, so that a subsequent adiabatic expansion can cool it to the nanokelvin temperature range.

DOI
10.1364/josab.6.002206

Related papers

Magnetic trapping and evaporative cooling of metastable triplet helium

Norbert Herschbach, Paul J. J. Tol, Andrey Tychkov +2 more

A cloverleaf magnetic trap is loaded from a magneto-optical trap containing 2 × 10 9 helium atoms in the metastable 2 3 S 1 state. With optical molasses and a spin polarization pulse up to 1.5 × 10 9 atoms are magnetically trapped. The vacuum limited trap lifetime is ∼12 s. Compression in 0.5 s yields a density increase to 8 × 10 9 cm −3 . With rf-forced evaporation using an exponentially shaped frequency sweep with a 5 s time constant the phase space density is increased from 1 × 10 −7 to 4 × 10 −3 . The central density increases to 3 × 10 11 cm −3 , while an increase in elastic collision rate from 40 to 220 s −1 indicates runaway evaporation.

Journal of Optics B Quantum and Semiclassical Optics•Apr 1, 2003•11 citations

Two-color magneto-optical trap for metastable helium

A. S. Tychkov, Jeroen C. J. Koelemeij, T. Jeltes +2 more

We describe a powerful scheme which combines laser cooling on two transitions of metastable helium to obtain a high phase-space density. By running a sequence of a large $1083\phantom{\rule{0.3em}{0ex}}\text{nm}$ magneto-optical trap (MOT) and a compressed $389\phantom{\rule{0.3em}{0ex}}\text{nm}$ MOT, a density increase of more than one order of magnitude is achieved within $5\phantom{\rule{0.3em}{0ex}}\text{ms}$. After compression, $8\ifmmode\times\else\texttimes\fi{}{10}^{8}$ atoms at a central density of $5\ifmmode\times\else\texttimes\fi{}{10}^{10}\phantom{\rule{0.3em}{0ex}}{\text{cm}}^{\ensuremath{-}3}$ remain, while the temperature of the cloud has been reduced from $1\phantom{\rule{0.3em}{0ex}}\text{mK}$ to $0.4\phantom{\rule{0.3em}{0ex}}\text{mK}$. The resulting phase-space density $(4.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6})$ is more than one order of magnitude higher than what we achieved by $1083\phantom{\rule{0.3em}{0ex}}\text{nm}$ laser cooling only.

Physical Review A•May 5, 2004•14 citations

Laser Cooling and Trapping of Neutral Atoms

Yvan Castin, Jean Dalibard, Claude N. Cohen-Tannoudji

We present a simple review of the basic physical processes allowing one to control, with laser beams, the velocity and the position of neutral atoms. The control of the velocity corresponds to a cooling of atoms, that is, a reduction of the atomic velocity spread around a given value. The control of the position means a trapping of atoms in real space. The best present performances will be given, in terms of the lowest temperatures and the highest densities. The corresponding highest quantum degeneracy will also be estimated. It is imposed by fundamental limits, which will be described briefly. We also give the general trends in this field of research and outline the new directions which look promising for observing quantum statistical effects in laser cooled atomic samples, but which are for the moment restricted by unsolved problems. Introducing the Simple Schemes The radiative forces acting on atoms in a light field can be split into two parts, a reactive one and a dissipative one. The dissipative force (radiation pressure), which basically involves scattering processes, is velocity dependent. We will see that this dependence leads to the Doppler cooling scheme and to the concept of optical molasses, and we will give the corresponding minimal achievable temperature. The dissipative force can be made position dependent, through a gradient of the magnetic field, so that the atoms are also trapped in the so-called magneto-optical trap.

Cambridge University Press eBooks•Apr 6, 1995•6 citations

Observation of a New Magneto-optical Trap

Olivier Émile, F Bardou, Ch Salomon +3 more

We report on the observation of a new laser trap for neutral atoms. It uses three orthogonal pairs of counterpropagating laser beams having linear polarizations at 45° and a quadrupole magnetic field. 10 8 cesium atoms were thus confined in a 0.15 mm 3 volume at a temperature of 60 μK, a factor of 2 below the Doppler cooling limit. We interpret this trapping as being due to the new magneto-optical force recently observed by Grimm et al. and which is essentially a dipole force rectified by the magnetic field. This trap opens new possibilities for increasing the phase-space density of laser-cooled atoms.

Europhysics Letters (EPL)•Dec 15, 1992•29 citations

Trapping fermionic and bosonic helium atoms

R. J. W. Stas

This thesis presents experimental and theoretical work performed at the Laser Centre of the Vrije Universiteit in Amsterdam to study laser-cooled metastable triplet helium atoms. Samples containing about 3x10^8 helium atoms-either fermionic helium-3 atoms, bosonic helium-4 atoms or mixtures thereof-are cooled to a temperature around 1 mK and form the starting point of the presented studies. The studies include an investigation of cold ionizing collisions in the absence of resonant light, an investigation of magneto-optical trapping with ultraviolet light, a feasibility study of an atomic fountain clock based on metastable helium-3 atoms and the first demonstration of magneto-optical trapping of an isotopic mixture of metastable helium atoms.

•Jun 1, 2005•1 citation

Laser cooling and trapping of atoms

G Townsend Christopher

 A detailed experimental and theoretical investigation of a magneto-optical trap for caesium atoms is presented. Particular emphasis has been placed on achieving high spatial number densities and low temperatures. Optimizing both of these together enables efficient evaporative cooling from a conservative trap, a procedure which has recently led to the first observations of Bose-Einstein condensation in a dilute atomic vapour. The behaviour of a magneto-optical trap is nominally determined by four independent parameters: the detuning and intensity of the light field, the magnetic field gradient and the number of trapped atoms. A model is presented which incorporates previous treatments into a single description of the trap that encompasses a wide range of its behaviour. This model was tested quantitatively by measuring the temperature of the cloud and its spatial distribution as a function of the four parameters. The maximum density was found to be limited both by the reabsorption of photons scattered within the cloud and by a reduction of the confining force at small light shifts. The nonlinear variation with position of the restoring force was found to be significant in limiting the number of atoms confined to a high density. A maximum density in phase space (defined as the number of atoms in a box with sides of dimension one thermal de Broglie wavelength) of (1.5 ± 0.5) x 10-5 was observed, with a spatial density of 1.5 x 1011 atoms per cm3. Cold collision losses from a caesium magneto-optical trap have been studied with the purpose of assessing their influence on spatial densities. In contrast to previous measurements of similar quantities, these measurements did not require the use of an ultra-low ( A study is presented of a modified magneto-optical trap in which a fraction of the population is shelved into a hyperfine level that does not interact with the trapping light. In this so-called dark magneto-optical trap, improved densities of nearly 1012cm-3 have been previously reported for sodium. The application of the technique to caesium is not straightforward due to the larger excited state hyperfine splittings. A simple theory for caesium is presented and its main predictions verified by measurements of density, number and temperature. A density of nearly 1012cm,-3 was indeed obtained but at a temperature substantially higher than in the conventional magneto-optical trap.

•Jan 1, 1995•1 citation
A quantitative discussion of several interesting and attractive properties of magneto-optical traps is presented. Calculations are given for the trap depth, sample size, and intrinsic cooling capability of this especially simple example of a radiative force trap. The discussion is directed toward the cooling and confinement of metastable 23S neutral helium, and a new loading procedure suitable for this atom is proposed. It is planned to operate the trap and to cool atoms in it with 1.08-μm light from solid-state, single-mode lasers pumped by efficient diode lasers. Because of the dissipative nature of the radiative force, a trapped sample of atoms may be magnetically compressed without increasing its millikelvin optical temperature, so that a subsequent adiabatic expansion can cool it to the nanokelvin temperature range.
A cloverleaf magnetic trap is loaded from a magneto-optical trap containing 2 × 10 9 helium atoms in the metastable 2 3 S 1 state. With optical molasses and a spin polarization pulse up to 1.5 × 10 9 atoms are magnetically trapped. The vacuum limited trap lifetime is ∼12 s. Compression in 0.5 s yields a density increase to 8 × 10 9 cm −3 . With rf-forced evaporation using an exponentially shaped frequency sweep with a 5 s time constant the phase space density is increased from 1 × 10 −7 to 4 × 10 −3 . The central density increases to 3 × 10 11 cm −3 , while an increase in elastic collision rate from 40 to 220 s −1 indicates runaway evaporation.
We describe a powerful scheme which combines laser cooling on two transitions of metastable helium to obtain a high phase-space density. By running a sequence of a large 1083nm1083\phantom{\rule{0.3em}{0ex}}\text{nm}1083nm magneto-optical trap (MOT) and a compressed 389nm389\phantom{\rule{0.3em}{0ex}}\text{nm}389nm MOT, a density increase of more than one order of magnitude is achieved within 5ms5\phantom{\rule{0.3em}{0ex}}\text{ms}5ms. After compression, $8\ifmmode\times\else\texttimes\fi{}{10}^{8}$ atoms at a central density of $5\ifmmode\times\else\texttimes\fi{}{10}^{10}\phantom{\rule{0.3em}{0ex}}{\text{cm}}^{\ensuremath{-}3}$ remain, while the temperature of the cloud has been reduced from 1mK1\phantom{\rule{0.3em}{0ex}}\text{mK}1mK to 0.4mK0.4\phantom{\rule{0.3em}{0ex}}\text{mK}0.4mK. The resulting phase-space density $(4.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6})$ is more than one order of magnitude higher than what we achieved by 1083nm1083\phantom{\rule{0.3em}{0ex}}\text{nm}1083nm laser cooling only.
We present a simple review of the basic physical processes allowing one to control, with laser beams, the velocity and the position of neutral atoms. The control of the velocity corresponds to a cooling of atoms, that is, a reduction of the atomic velocity spread around a given value. The control of the position means a trapping of atoms in real space. The best present performances will be given, in terms of the lowest temperatures and the highest densities. The corresponding highest quantum degeneracy will also be estimated. It is imposed by fundamental limits, which will be described briefly. We also give the general trends in this field of research and outline the new directions which look promising for observing quantum statistical effects in laser cooled atomic samples, but which are for the moment restricted by unsolved problems. Introducing the Simple Schemes The radiative forces acting on atoms in a light field can be split into two parts, a reactive one and a dissipative one. The dissipative force (radiation pressure), which basically involves scattering processes, is velocity dependent. We will see that this dependence leads to the Doppler cooling scheme and to the concept of optical molasses, and we will give the corresponding minimal achievable temperature. The dissipative force can be made position dependent, through a gradient of the magnetic field, so that the atoms are also trapped in the so-called magneto-optical trap.
We report on the observation of a new laser trap for neutral atoms. It uses three orthogonal pairs of counterpropagating laser beams having linear polarizations at 45° and a quadrupole magnetic field. 10 8 cesium atoms were thus confined in a 0.15 mm 3 volume at a temperature of 60 μK, a factor of 2 below the Doppler cooling limit. We interpret this trapping as being due to the new magneto-optical force recently observed by Grimm et al. and which is essentially a dipole force rectified by the magnetic field. This trap opens new possibilities for increasing the phase-space density of laser-cooled atoms.
This thesis presents experimental and theoretical work performed at the Laser Centre of the Vrije Universiteit in Amsterdam to study laser-cooled metastable triplet helium atoms. Samples containing about 3x10^8 helium atoms-either fermionic helium-3 atoms, bosonic helium-4 atoms or mixtures thereof-are cooled to a temperature around 1 mK and form the starting point of the presented studies. The studies include an investigation of cold ionizing collisions in the absence of resonant light, an investigation of magneto-optical trapping with ultraviolet light, a feasibility study of an atomic fountain clock based on metastable helium-3 atoms and the first demonstration of magneto-optical trapping of an isotopic mixture of metastable helium atoms.
 A detailed experimental and theoretical investigation of a magneto-optical trap for caesium atoms is presented. Particular emphasis has been placed on achieving high spatial number densities and low temperatures. Optimizing both of these together enables efficient evaporative cooling from a conservative trap, a procedure which has recently led to the first observations of Bose-Einstein condensation in a dilute atomic vapour. The behaviour of a magneto-optical trap is nominally determined by four independent parameters: the detuning and intensity of the light field, the magnetic field gradient and the number of trapped atoms. A model is presented which incorporates previous treatments into a single description of the trap that encompasses a wide range of its behaviour. This model was tested quantitatively by measuring the temperature of the cloud and its spatial distribution as a function of the four parameters. The maximum density was found to be limited both by the reabsorption of photons scattered within the cloud and by a reduction of the confining force at small light shifts. The nonlinear variation with position of the restoring force was found to be significant in limiting the number of atoms confined to a high density. A maximum density in phase space (defined as the number of atoms in a box with sides of dimension one thermal de Broglie wavelength) of (1.5 ± 0.5) x 10-5 was observed, with a spatial density of 1.5 x 1011 atoms per cm3. Cold collision losses from a caesium magneto-optical trap have been studied with the purpose of assessing their influence on spatial densities. In contrast to previous measurements of similar quantities, these measurements did not require the use of an ultra-low ( A study is presented of a modified magneto-optical trap in which a fraction of the population is shelved into a hyperfine level that does not interact with the trapping light. In this so-called dark magneto-optical trap, improved densities of nearly 1012cm-3 have been previously reported for sodium. The application of the technique to caesium is not straightforward due to the larger excited state hyperfine splittings. A simple theory for caesium is presented and its main predictions verified by measurements of density, number and temperature. A density of nearly 1012cm,-3 was indeed obtained but at a temperature substantially higher than in the conventional magneto-optical trap.