Narrowing of the coherent population trapping resonance under zone pumping in cells with different characteristics of the wall coating

It is shown that when coherent population trapping (CPT) resonance is excited by a narrow laser beam, the presence of elastic collisions with the cell wall significantly affects the line shape of the CPT-resonance. We have constructed a theoretical model, which is based on averaging over the random Ramsey sequences of the atom dwell time in the beam and dark zones and takes into account the probability of elastic bounce of an atom from the wall.