Magneto-optical Trapping of Cr Atoms
Magneto-optically trapped cloud of Cr atoms
A key technique that represents a gateway into the highest level of control over neutral atoms is
magneto-optical trapping. Six circularly-polarized laser beams, tuned just below an atomic resonance,
are aimed at the center of a region with increasing magnetic field in all directions. The laser beams
slow atoms as they approach the trap, and keep them in the center by light pressure that is spatially
dependent because of the magnetic field gradient. Because of the efficiencies associated with laser
cooling, the trapped population of atoms can have temperatures of less than 100 microkelvin and can be
localized to a few micrometers. This population of cold atoms is an excellent starting point for
further cooling, for example to create a
Bose-Einstein condensate, or as an easily controllable source of neutral atoms for nanotechnology.
Magneto-optical traps have been demonstrated for several atomic species, in particular the alkalis and
the rare gases. But before the present work, a chromium trap had never been demonstrated. Chromium poses
some special problems because there are optical leaks from the excited 7Po4
state to the metastable 5D3 and 5D4 states
(see spectrum here). However, it is of
particular interest from a nanotechnological point of view because of its growth properties, its
role as an optical dopant, and its extremely large magnetic moment.
Using two diode lasers tuned to 653.97 nm and 663.18 nm to plug these optical leaks, we have been
able to trap over 106 atoms and have achieved densities as high as 1016
m-3 [EPG Pub# 710]. Since its first
demonstration, the Cr magneto-optical trap has proven to be an excellent venue for developing
deterministic atom sources. Future
work will involve developing these sources, and also investigating cold collisions in a molecular
system with rich electronic structure.
Magneto-Optical Trapping of Chromium Atoms
Jabez J. McClelland - NIST
Curtis Bradley -
Petroleum Institute, Dubai
William Anderson - Lighthouse, Inc.
Shannon Hill - NIST
Marin Pichler - Goucher College
Online: August 1995
Last update: February 2008
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