Enhancement of gain in inversionless atomic media using finite bandwidth driving fields

We explore the possibility of enhancing the gain in lasing without inversion schemes by replacing the usual incoherent pump with a finite bandwidth (spectrally coloured) pump. Three level atoms in the ladder and lambda configuration are modelled and we find that replacing the incoherent pump with a partially coherent pump amplifies the gain by as much as a factor of 4. The results are obtained via Monte-Carlo simulations of the density matrix equations, which, for a coloured pump, have the form of Langevin equations. We find that for a given set of atom-field parameters, the gain for coherent pumping is larger than for incoherent pumping, and that maximum gain is obtained for a partially coherent pump. The frequency of the coloured pump plays an important role in determining the optimum gain that can be obtained.