Line shape of coherent population trapping resonance in the Λ-scheme under Ramsey-type interrogation in an optically dense medium

We report a study of the Ramsey technique for detecting coherent population trapping resonance in a cold rarified ensemble of atoms with the collective effects related to its finite optical thickness taken into account. It is found that with the growth of the optical thickness of the medium the Ramsey comb becomes shifted with its maxima 'trimmed'. The possibility of producing a region of maximal atomic excitation near the exit from the medium is found.