Control of amplification without population inversion in H2 and Li2 molecules:: three level Ladder, V and Λ systems

We have studied (ab-initio) the feasibility of Amplification Without Population Inversion (AWPI) both numerically and analytically, in H-2 and Li-2 molecules for three different three level schemes e.g. (i) Ladder, (ii) V and (iii) A. We have shown that the shape of the gain profile (gain as a function of the detuning from upper lasing level) and its magnitude are different for these three transition schemes. We have also shown that the strength of AWPI and its variation with detuning can be controlled by choosing different vibrational levels of the molecule as the upper and lower levels for amplification. Thus AWPI can be obtained in a wide range of frequencies considering transitions between different vibrational levels within the same set of electronic states, in contrast to that in atoms. For three level ladder system, time evolution of gain profile shows that for resonant transitions AWPI can be obtained only for short time duration. It has been shown that AWPI is also feasible in presence of Doppler broadening (which is orders of magnitude greater than the spontaneous decay width in H-2 and Li-2 molecules) if the coherent coupling strength is increased by orders of magnitude.