  We propose a method for the determination of the interaction potential of
Rydberg atoms. Specifically, we consider a laser-driven Rydberg gas confined in
a one-dimensional lattice and demonstrate that the Rydberg atom number after a
laser excitation cycle as a function of the laser detuning provides a measure
for the Rydberg interaction coefficient. With the lattice spacing precisely
known, the proposed scheme only relies on the measurement of the number of
Rydberg atoms and thus circumvents the necessity to map the interaction
potential by varying the interparticle separation.
