COHERENT POPULATION TRAPPING AT LOW-LIGHT LEVELS

A three-level lambda (Lambda) system driven by two coherent fields at the Raman resonance condition evolves to a nonabsorbing eigenstate of the Hamiltonian called the coherent population trapping (CPT) state. W e study the various factors dictating the dynamical evolution of the c oherencesand the populations to the CPT state. We demonstrate the form ation of the CPT state even at low intensities, though it takes much l onger to form such a state. For the case of unequal decay rates we dem onstrate an interesting sharp dip in the steady-state response of the medium at the Raman resonance condition.