Spectroscopy of Trapped Ions and Atoms

Because of the detuning of the laser, a photon can only be absorbed when the ion moves against the laser beam. The absorption of the momentum p = hu/c of the photon will slow down the ion. The decay photon can be emitted in any direction. After some time, the ion has been brought to a very low velocity. A photograph of the fluorescence of a single Ba+ ion is shown in Fig.9.53a. In Fig.9.53b the crystallization of a few Mg ions in a trap is illustrated. The atoms are cooled to such a low velocity that the electrostatic forces between the ions dominate and an ordered arrangement is obtained [9.218]. 

We have above discussed certain mechanical actions on atoms induced by laser light. Using resonance-radiation pressure atomic beams can also be focused and manipulated in interesting ways [9.233,234]. Several other interesting mechanical effects exist and have been explored. Studied phenomena include light diffusive pulling [9.235], light-induced drift [9.236] and the optical piston [9.237]. 

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