To perform depletion spectroscopy, a radiating core-excited level is used as a reference level from which to access the autoionizing manifold, as illustrated in the figure. The radiating level is impulsively excited, and a detector monitors
the resulting fluorescence from this level. A tunable
dye laser is passed through the excited vapor to transfer
the fluorescing atoms to other core-excited levels nearby.
As the laser is scanned in frequency, a level is encountered,
and the excited population is transferred to it, resulting in
a depletion in the amount of fluorescence observed from
the reference level. The location of the depletion signal, as
a function of dye laser frequency, determines the energy of
the accessed level, relative to the reference level. The shape
of the depleted signal, as a function of laser intensity, can
be analyzed to determine the oscillator strength and Lorentz
width of the transition.