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arXiv:cond-mat/0505709 · Physical Review A

Evaporative cooling of a guided rubidium atomic beam

Thierry Lahaye, Zhongde Wang, Gael Reinaudi, Steffen Patrick Rath, Jean Dalibard, David Guéry-Odelin

Published Sep 19, 2005• 35 citations
arXivHTMLPDF

Abstract

We report on our recent progress in the manipulation and cooling of a magnetically guided, high-flux beam of $^{87}\mathrm{Rb}$ atoms. Typically, $7\ifmmode\times\else\texttimes\fi{}{10}^{9}\phantom{\rule{0.3em}{0ex}}\text{atoms}\phantom{\rule{0.3em}{0ex}}\text{per}\phantom{\rule{0.3em}{0ex}}\text{second}$ propagate in a magnetic guide providing a transverse gradient of $800\phantom{\rule{0.3em}{0ex}}\mathrm{G}∕\mathrm{cm}$, with a temperature $\ensuremath{\sim}550\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{K}$, at an initial velocity of $90\phantom{\rule{0.3em}{0ex}}\mathrm{cm}∕\mathrm{s}$. The atoms are subsequently slowed down to $\ensuremath{\sim}60\phantom{\rule{0.3em}{0ex}}\mathrm{cm}∕\mathrm{s}$ using an upward slope. The relatively high collision rate $(5\phantom{\rule{0.3em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1})$ allows us to start forced evaporative cooling of the beam, leading to a reduction of the beam temperature by a factor of 4, and a tenfold increase of the on-axis phase-space density.

DOI
10.1103/physreva.72.033411

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In this paper, we report our progress towards the realization of a continuous guided atomic beam in the degenerate regime. So far, we have coupled into a magnetic guide a flux of a few 10810^{8}108 atoms/s at 60 cm/s with a propagation in the guide over more than 2 meters. At this stage, the collision rate is not high enough to start an efficient forced evaporative cooling. Here we describe a new approach to reach the collisional regime. It is based on a pulsed feeding of the magnetic guide at a high repetition rate. The overlap of the packets of atoms occurs in the guide and leads to a continuous guided beam. We discuss different ways to increase the collision rate of this beam while keeping the phase space density constant by shaping the external potential.
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We discuss the implementation and characterization of the source of a slow, intense, and collimated beam of rubidium atoms. The cold atomic beam is produced by two-dimensional magneto-optical trapping in directions transverse to the atomic beam axis and unbalanced Doppler cooling in the axial direction. The vacuum design allows use of relatively low laser power and a considerably simplified assembly. The atomic beam has a high flux of about $2\ifmmode\times\else\texttimes\fi{}{10}^{10}\phantom{\rule{0.3em}{0ex}}\mathrm{atoms}∕\mathrm{s}$ at a total cooling laser power of 55mW55\phantom{\rule{0.3em}{0ex}}\mathrm{mW}55mW. It has a narrow longitudinal velocity distribution with mean velocity 15m∕s15\phantom{\rule{0.3em}{0ex}}\mathrm{m}∕\mathrm{s}15m∕s with full width at half maximum 3.5m∕s3.5\phantom{\rule{0.3em}{0ex}}\mathrm{m}∕\mathrm{s}3.5m∕s and has a low divergence of 26mrad26\phantom{\rule{0.3em}{0ex}}\mathrm{mrad}26mrad. The high flux enables ultrafast loading of about 1010{10}^{10}1010 atoms into a three-dimensional (3D) magneto-optical trap within 500 ms. The variation of the atomic beam flux was studied as a function of the rubidium vapor pressure, cooling laser power, transverse cooling laser beam length, detuning of the cooling laser, and relative intensities of the cooling beams along the atomic beam axis. We also discuss a detailed comparison of our measurements of the cold atomic beam with a 3D numerical simulation.
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