Spatial Distribution of Excited States

Yacoub Makdisi, K. S. Bhatia, J P Connerade

We review several new optical techniques which reveal the spatial distribution of excited atomic states. These techniques have been developed in different laboratories, largely as a result of exploiting laser excitation, which provides additional flexibility in the choice of excitation paths. Several methods are in use, which possess different advantages, but all share one common property. They sample the wavefunction of the excited state at different radii using different excitation paths, and are thereby sensitive to size. Amongst the radial phenomena which control the size of an atomic orbital, the most important are the centrifugal barrier effects which determine orbital collapse.

V. S. Vorob’ev

G. Lochead

This thesis describes the development of a new technique for measuring the spatial distribution of Rydberg atoms in a cold strontium gas. Strontium atoms are cooled and trapped in a magneto-optical trap and coherently excited to Rydberg states in a two-photon, three-level ladder scheme. Several methods of stabilizing the frequency to the cooling transition are discussed and characterized. A frequency stabilization scheme based on electromagnetically-induced transparency for the second laser required for Rydberg excitation is also explained. The Rydberg population dynamics are studied experimentally and modeled using an optical Bloch equation simulation. The divalent nature of strontium allows doubly excited “autoionizing” states to be accessed using resonant optical excitation. These states ionize in subnanosecond timescales, with the ions recorded on a micro-channel plate being proportional to the amount of Rydberg atoms. Translation of an autoionizing laser focused to a waist of 10 μm gives a spatially resolved Rydberg signal. A two-dimensional map of the Rydberg spatial distribution has been made using this autoionizing microscopy technique.

L. M. Biberman, V. S. Vorob’ev, I. T. Yakubov

Ya. A. Fofanov, A. S. Kuraptsev, Igor M. Sokolov +1 more

On the basis of our general theoretical results developed previously [I. M. Sokolov et al., J. Exp. Theor. Phys. 112, 246 (2011)], we calculate the spatial distribution of atoms excited in a dense and cold atomic cloud by weak monochromatic light. We also study the atomic distribution over different Zeeman sublevels of the excited state in different parts of the cloud. The dependence of this distribution of atomic excitation on the density of the atomic ensemble and the frequency of external emission is investigated. We show that in the boundary regions of the cloud, the orientation and alignment of atomic angular momentum takes place. Analysis of the spatial distribution of atomic excitation shows no noticeable signs of light localization effects, even in those parameter regimes where the Ioffe-Regel criterium of strong localization is satisfied. However, comparative calculations performed in the framework of the scalar approximation to the dipole-dipole interaction reveal explicit manifestation of strong localization under some conditions.