  We experimentally investigated the characteristics of two-photon transmission
resonances in Rb vapor cells with different amount of buffer gas under the
conditions of steady-state coherent population trapping (CPT) and pulsed
Raman-Ramsey (RR-) CPT interrogation scheme. We particularly focused on the
influence of the Rb atoms diffusing in and out of the laser beam. We showed
that this effect modifies the shape of both CPT and Raman-Ramsey resonances, as
well as their projected performance for CPT clock applications. In particular
we found that at moderate buffer gas pressures RR-CPT did not improved the
projected atomic clock stability compare to the regular steady-state CPT
resonance.
