  Selective field ionization is used to determine the state or distribution of
states to which a Rydberg atom is excited. By evolving a small perturbation to
the ramped electric field using a genetic algorithm, the shape of the
time-resolved ionization signal can be controlled. This allows for separation
of signals from pairs of states that would be indistinguishable with
unperturbed selective field ionization. Measurements and calculations are
presented that demonstrate this technique and shed light on how the
perturbation directs the pathway of the electron to ionization. Pseudocode for
the genetic algorithm is provided. Using the improved resolution afforded by
this technique, quantitative measurements of the
$36p_{3/2}+36p_{3/2}\rightarrow 36s_{1/2}+37s_{1/2}$ dipole-dipole interaction
are made.
