PROBING THE SPATIAL-DISTRIBUTION OF EXCITED ATOMIC STATES

We review several new optical techniques which reveal the spatial dist ribution of excited atomic states. These techniques have been develope d in different laboratories, largely as a result of exploiting laser e xcitation, which provides additional flexibility in the choice of exci tation paths. Several methods are in use, which possess different adva ntages, but all share one common property. They sample the wavefunctio n of the excited state at different radii using different excitation p aths, and are thereby sensitive to size. Amongst the radial phenomena which control the size of an atomic orbital, the most important are th e centrifugal barrier effects which determine orbital collapse.