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Europhysics Letters (EPL)

Raman cooling of spin-polarized cesium atoms in a crossed dipole trap

Hélène Perrin, Axel Kuhn, Isabelle Bouchoule, Tilman Pfau, Ch Salomon

Published Apr 15, 1999• 18 citations
Publisher

Abstract

We describe a Raman cooling scheme that allows for the simultaneous polarization and cooling of cesium atoms. Using efficient chirped Raman pulses, cesium atoms confined in a red-detuned crossed dipole trap are 80 % polarized and cooled to a temperature of 2.4 μK. After cooling, the phase-space density reaches 10 −3 . We have strong evidence that this value is limited by multiple photon scattering within the atomic cloud.

DOI
10.1209/epl/i1999-00236-0

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We describe a Raman cooling scheme that allows for the simultaneous polarization and cooling of cesium atoms. Using efficient chirped Raman pulses, cesium atoms confined in a red-detuned crossed dipole trap are 80 % polarized and cooled to a temperature of 2.4 μK. After cooling, the phase-space density reaches 10 −3 . We have strong evidence that this value is limited by multiple photon scattering within the atomic cloud.
We trap 107{10}^{7}107 cesium atoms in a far red detuned 1D optical lattice. With degenerate Raman sideband cooling we achieve a vibrational ground state population of 80% for the steep trapping direction. Collisional coupling enables us to cool the spin-polarized gas in 3D without loss of atoms to a peak phase space density of 1/1801/1801/180 at a mean temperature of $2.8\ensuremath{\mu}\mathrm{K}$ and a density of $1.4\ifmmode\times\else\texttimes\fi{}{10}^{13}{\mathrm{cm}}^{\ensuremath{-}3}$.
We have simultaneously spin polarized and subrecoil cooled sodium atoms trapped in a blue detuned optical dipole trap. Temperatures of 1.5 \ensuremath{\mu}K and less have been achieved for atoms which have been polarized into any of three F=1F=1F=1 ground-state magnetic sublevels of sodium. The final phase-space density is comparable to the best achieved by an all-optical cooling technique.
We present a new and efficient implementation of Raman cooling of trapped atoms. It uses Raman pulses with an appropriate frequency chirp to realize a velocity selective excitation through a rapid adiabatic passage. This method allows to address in a single pulse a large number of non zero atomic velocity classes and it produces a nearly unity transfer efficiency. We demonstrate this cooling method using cesium atoms in a far-detuned crossed dipole trap. Three-dimensional cooling of 1×1051 \times 10^{5}1×105 atoms down to 2μ2 μ2μK is performed in 100 ms. In this preliminary experiment the final atomic density is 1.3×10121.3\times 10^{12}1.3×1012 at/cm3^33 (within a factor of 2) and the phase-space density increase over the uncooled sample is 20. Numerical simulations indicate that temperatures below the single photon recoil temperature should be achievable with this method.
We have Raman cooled sodium atoms below the photon recoil temperature in a novel type of blue-detuned optical dipole force trap. In this trap $4.5\ifmmode\times\else\texttimes\fi{}{10}^{5}$ atoms have been cooled to an effective three dimensional temperature of 1.0 \ensuremath{\mu}K at a final density of $4\ifmmode\times\else\texttimes\fi{}{10}^{11}{\mathrm{cm}}^{\ensuremath{-}3}$. No atoms were lost during the cooling process. The phase space density increased by a factor of 320 over the uncooled sample. This is the highest phase space density achieved by an all-optical cooling method.
We develop a simple and practical scheme to apply sideband cooling to a cloud of rubidium atoms. A sample containing 4 × 10 70 87 Rb is trapped in a far red detuned optical lattice. Through optimizing the relevant parameters, i.e., laser detuning, magnetic field, polarization, and duration time, a temperature around 1.5 μK and phase space density close to 1/500 are achieved. Compared with polarization gradient cooling, the temperature decreases by around one order of magnitude. This technique could be used in high precision measurement such as atomic clocks and atom interferometer. It could also serve as a precooling means before evaporation cooling in a dipole trap, and may be a promising method of achieving quantum degeneracy with purely optical means.
We demonstrate a simple, general purpose method to cool neutral atoms. A sample containing $3\ifmmode\times\else\texttimes\fi{}{10}^{8}$ cesium atoms prepared in a magneto-optical trap is cooled and simultaneously spin polarized in 10 ms at a density of $1.1\ifmmode\times\else\texttimes\fi{}{10}^{11}\mathrm{cm}{}^{\ensuremath{-}3}$ to a phase space density $n{\ensuremath{\lambda}}_{\mathrm{dB}}^{3}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1/500$, which is almost 3 orders of magnitude higher than attainable in free space with optical molasses. The technique is based on 3D degenerate Raman sideband cooling in optical lattices and remains efficient even at densities where the mean lattice site occupation is close to unity.