Steep dispersion in coherent population trapping with losses

The dispersive properties of coherent population trapping with losses are i nvestigated. We consider a cold sample of open three-level atoms interactin g with two laser fields in the Lambda configuration. We show that despite t he population losses the slope of the dispersion at Raman resonance reaches at large interaction time a constant nonzero value. A numerical study of t he propagation of a pulse in the medium in the presence of a strong couplin g field shows that very small group velocities for the pulse are obtained a lso in the presence of population losses. (C) 2000 Elsevier Science B.V. Al l rights reserved.