Photoassociation of Laser-cooled Atoms: A New Spectroscopy

Advances in laser cooling and trapping have allowed researchers to begin to explore the field of ultracold collisions. An important new development is the technique of ultracold photoassociative spectroscopy. The idea was proposed by Thorsheim et al. in 1987 but has only been realized experimentally within the last two years. In photoas-sociative spectroscopy, free atoms that are held in an optical trap collide. During the collision, the free atoms are promoted by laser excitation to bound molecular states. These excited molecules can then either be ionized with an additional photon and detected or allowed to decay into hot atoms that escape the trap. The photoassociation in this latter case is monitored by means of the increased loss of atoms from the trap. An example of the two types of spectra is shown in the figure. Extremely precise spectroscopy of the created dimers can be performed in this way.

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