Probing the spatial distribution of excited atomic states
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.