Ground-state grating echoes from Rb vapor at room temperature

We have used two sets of opposite circularly polarized traveling wave pulses separated in time to establish, and subsequently rephase, a spatially modulated coherence between the magnetic sublevels of the [Formula Presented] ground state in Doppler broadened [Formula Presented] vapor. The rephasing results in a magnetic grating echo whose duration is an accurate measure of the velocity distribution. We demonstrate that the time scale of the experiment is determined solely by the transit time of atoms across the laser beam. The shortening of the lifetime due to a perturber (Ar) allows us to infer the Rb-Ar velocity changing collision cross section.