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Physical Review Letters

Transverse Diffusion in Isotropic Light Slowing

T.G. Aardema, R. M. S. Knops, S. P. L. Nijsten, K. A. H. van Leeuwen, Jan P. J. Driessen, Herman C. W. Beijerinck

Published Jan 29, 1996• 8 citations
Publisher

Abstract

We have demonstrated the slowing of a beam of cold (180 K) metastable neon atoms in a diffuse reflecting cylindrical cavity with monochromatic light. Using a well-collimated atomic beam entering the cavity, it is shown that stimulated emission has a major effect on the transverse velocity distribution. A large saturation parameter $s$ results in a loss mechanism for the center line beam intensity. A Monte Carlo simulation shows that the light intensity should be evenly distributed with moderate saturation conditions, to optimize the slowing effect while minimizing the transverse diffusion.

DOI
10.1103/physrevlett.76.748

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We have demonstrated the slowing of a beam of cold (180 K) metastable neon atoms in a diffuse reflecting cylindrical cavity with monochromatic light. Using a well-collimated atomic beam entering the cavity, it is shown that stimulated emission has a major effect on the transverse velocity distribution. A large saturation parameter sss results in a loss mechanism for the center line beam intensity. A Monte Carlo simulation shows that the light intensity should be evenly distributed with moderate saturation conditions, to optimize the slowing effect while minimizing the transverse diffusion.
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The transverse cooling of a beam of sodium atoms in an axisymmetric light field formed by a reflecting axicon is studied. It is shown that transverse cooling leads to a decrease in angular divergence (collimation) of the atomic beam. The transverse velocities of the beam are reduced from 5.5 × 102 to 1.6 × 102 cm/sec, which corresponds to the decrease in effective transverse temperature of the beam from T = 42 to T = 3.3 mK. The spatial and velocity distributions of the atomic beam are calculated numerically. It is found that theory and experiment are in good agreement.
We have developed a ``beam brightener'' in which several different laser cooling methods produce a highly monochromatic, unidirectional and intense beam of metastable Ne(3s;^3P_2) atoms. The beam brightener consists of four main stages. From an exited neon source we capture in a collimating section 5× 10^11 Ne(3s)/s from which ≈ 50 % is slowed to 100 m/s in a Zeeman slower. The final velocity distribution shows a width of 3.3 m/s uc(RMS,) corresponding to a temperature of 12 mK. A fraction of ≈ 25 % of these cold atoms is captured by a magneto-optic compressor and molded into a 0.7 mm uc(FWHM) wide atomic beam that contains up to 5× 10^10 Ne(3s)/s. The resulting density is 1.1× 10^9 Ne(3s)/cm^3. In the final step, a Doppler cooler is used to minimize the divergence of the beam to 10 mrad. This value will further improve once the Doppler cooler is replaced by a sub-Doppler cooler. We plan to use this ``bright beam'' to investigate the ionization probabilities in Ne(3s)+Ne(3s) collisions. Emphasis will be on the suppression of ionization when the atoms are spin-polarized. This has important implications for the possibilities of using metastable atoms for BEC-type experiments. Present adress: NIST
We present experimental and theoretical studies of polarization-gradient cooling of metastable neon atoms confined to the dark center of a TEM01∗{\mathrm{TEM}}_{01}^{*}TEM01∗​ (doughnut) mode. A slow beam of neon atoms is guided and focused inside a blue-detuned and focused doughnut-mode laser beam to a spot size below 10 \ensuremath{\mu}m. The transverse motion inside this doughnut mode is cooled by means of two-dimensional optical molasses. We observed non-Gaussian two-component velocity distributions of which the cold component has a width of down to three recoil velocities. These results are found to be in qualitative agreement with a quantum Monte Carlo simulation of cooling in one dimension in the presence of an external light-shift potential. For the simulation we apply the recently developed technique of quantum-state diffusion with adaptive noise.