University of Groningen
Laser cooling and trapping of barium
De, Subhadeep
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Publication date:
2008
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De, S. (2008). Laser cooling and trapping of barium s.n.
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Summary
First laser cooling and trapping of the heavy alkaline-earth element barium has
been achieved. The cooling cycle using the strong 6s2 1 S0 → 6s6p 1 P1 transition
at wavelength λ1 = 553.7 nm exhibits large leaks to metastable D-states. This
makes laser trapping with this transition only impossible. Additional lasers are
thus needed to bring the atoms back in to the cooling cycle. In total seven lasers
were employed to confine barium atoms in a magneto-optical trap (MOT) (see
Fig.C.1).
The properties of the barium MOT were characterized. The efficiency of
capturing an atom from a thermal atomic beam into the MOT is 0.4(1)%. Loss
rate mechanisms from the trap were studied by observing the decay of the trap
population. Typical lifetimes of the MOT cloud are on the order of one second
and are limited mainly due to insufficient repumping of D-states. The trapping
efficiency and the trap lifetimes may be improved by employing more powerful
lasers for repumping. The range of velocities from which barium atoms can
be captured into the MOT is about 30 m/s. The velocity capture range could
be widened significantly with an intense broadband laser light source in future.
Different laser transitions were employed for repumping barium atoms from the
6s5d 3 D1 and the 6s5d 3 D2 states. They lead to similar trap populations and
lifetimes. The temperature of the cold atomic barium cloud was determined to
about 5 mK. This is about ten times larger than the Doppler limit known from
the theory of laser cooling. Atomic properties of the 5d2 3 F2 state were studied
with trapped atoms, in particular it’s lifetime was determined as 160(10)µs.
This work has shown a possible scheme to trap atoms with a leaky cooling
cycle. Since atoms with such properties are the majority of the elements in the
periodic table, the number of optically trapable elements can be significantly
enlarged. Of particular high interest is radium, the chemical homologue to barium. The techniques developed here can be used to build an efficient collection
MOT for radium using the strong 7s2 1 S0 → 7s7p 1 P1 transition as primary cool-
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Summary
Count rate [1/s]
2
x 10
8
1.5
1
0.5
(b)
(a)
0
Trapped barium
-60
-40
t
∆ν
1
-20
[MHz]
0
Fig. C.1: (a) Photograph of a cold could of barium atoms in a magneto-optical
trap. The bright spot at the center of the optical port is scattered light at wavelength 553.7 nm of the cooling transition. (b) Dependence of the MOT fluorescence
on the frequency detuning ∆ν1t of the trapping laser beams at wavelength 553.7 nm.
ing transition. The interest in radium stems from it’s high sensitivity to possible
nuclear and electron permanent electric dipole moments (EDM’s). An EDM violates parity as well as time reversal and is therefore of fundamental importance.
Searches for such EDM’s are among the main research goals of the recently commissioned TRIµP facility at KVI.