A trap relying on optical pumping
P. Bouyer, J. Dalibard, P. Lemonde, A.
Michaud, M. Ben Dahan, C. Salomon
École Normale Supérieure, Lab.
Kastler-Brossel, 24 rue Lhomond, Paris
CEDEX 75231, France
in: Proceedings EQEC. 29 aug-2 sept 1994, pp. 2-3 (1994) (reference)
The usual way of obtaining laser cooled atoms at high densities is to use a magneto-optical trap.1 In such a spontaneous force trap, the optical Earnshaw theorem is circumvented2,3
by use of a magnetic fiend gradient together with optical pumping.
Unfortunately, in many experiments such as frequency standards or
sub-recoil cooling,4,5 this magnetic field may cause severe
limitations, owing to the difficulty of removing residual fields after
the operation of the magneto-optical trap.
We have investigated a new kind of radiation
pressure that requires no magnetic field and also circumvents the
Earnshaw theorem by optical pumping, this trap consists of six
circularly polarized divergent beams (Fig. 1) and works on the red of
a Jg --> Je = Jg+1 atomic transition with Jg > 1/2.
The spatially varying intensity leads to a position dependent optical
pumping and creates a restoring force on an atom displaced from the
We have demonstrated this trap in a vapor cell using the 852-nm cesium Jg=4 --> Je=5
transition. The performance of this trap in terms of number
of trapped atoms is within one order of magnitude of that of an
optimized magneto-optical trap employing the same laser beams In our
preliminary experiments, we have trapped up to 5 × 107 atoms in a 300 µm 1/e1/2 radius trap at about 40 µK and an average density of 1011 at/cm3.
1 - Experimental set-up: Each circularly polarized 20 mW 852-nm laser
beam is focused at 3.5 cm from the center of the trap using six
objectives with N.A.=0.4. At a detuning of -10 MHz, the trap contains
~5 × 107 atoms.
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