  We report on experiments exploring Stark-tuned F\"orster resonances between
Rydberg atoms with unprecedented resolution in the F\"orster defect. The
individual resonances are expected to exhibit different angular dependencies,
opening the possibility to tune not only the interaction strength but also the
angular dependence of the pair state potentials by an external electric field.
We achieve a high resolution by optical Ramsey interferometry for Rydberg atoms
combined with electric field pulses. The resonances are detected by a loss of
visibility in the Ramsey fringes due to resonances in the interaction. We
present measurements of the density dependence as well as of the coherence time
at and close to F\"orster resonances.

Atomic Physics