Interaction of a sequence of frequency-chirped bichromatic laser pulses with an ensemble of Λ-atoms:: Population trapping and coherent optical pumping

We show that population trapping may be achieved in an ensemble of Doppler-broadened three-level Lambda-atoms when acting by a few frequency-chirped bichromatic laser pulses (BLPs) with duration longer than the decay time of the excited state of the atoms. The action of successive sequence of short frequency-chirped laser pulses on such a prepared atomic ensemble results in coherent optical pumping of atoms into a single ground state. A reversible population transfer between two ground states of the atoms through an intermediate specific distribution of populations between the atomic states is shown to be produced by a sequence of frequency-chirped short BLPs.