Nichtlineare Optik und Quantenoptik (Prof. Dr. W. Lange, HDoz. Dr. T. Ackemann)
Transverse Nonlinear Optics in Samples of Cold Atoms
It is well known that intense laser beams propagating in nonlinear media can self-focus. This phenomenon
occurs in media in which the refractive index increases with increasing intensity. Therefore, the center part of a
beam experiences a phase retardation with respect to the wings which causes the beam to focus. This effect can
even result in the destruction of the material.
We performed previously detailed experimental
and theoretical investigations on the mechanism and strength of the lensing effect using sodium in a hot vapor
cell (about 580 K). Recent activity concerns nonlinear beam shaping effects in ensembles of cold,
laser-cooled atoms (< 100 µK). This system is attractive because it is very clean and thus a comparison
between experiment and theory is facilitated. In addition, there are fascinating possibilities for new forms of
optical self-organization due to the coupling of the center of mass movement of cold atoms to inhomogenous, in
particular modulated, light fields. The experiments
are performed in a high-density magneto-optical trap with rubidium atoms at the Institut Non Lineaire de Nice.
Our experiment yielded the first experimental evidence for nonlinear beam shaping in an ensemble of cold atoms.
Current activity is on further characterization and the possibility of more complex forms of self-organization.
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