H. M. Doss

A simple model of a laser without inversion

Abstract We consider a simple model of a four level atom as a candidate for laser action without population inversion. Our system has a degenerate or quasi-degenerate ground state doublet and two higher excited states; one of these higher levels is coupled to the ground states by a coherent field of variable strength, whose role is to create atomic coherence between the lowest levels; the other is also coupled to the ground states but only when laser action develops. This model includes an incoherent pump mechanism to produce some population in the top lasing state. We calculate the absorption profile of the laser transition and identify the conditions under which gain may develop. We find that gain is available over a suitable range of values of the driving field strength and incoherent pump rates. The shape of the gain profile and the frequency at which the profile is maximum change as one varies the operating conditions. We provide a physical interpretation of our results with the help of a convenient set of dressed atomic states.

Physical origin of the gain in a four-level model of a Raman driven laser without inversion

Abstract The aim of this communication is to provide additional insight into the physical origin of the gain in a four-level model of a Raman driven laser without inversion. With the help of an appropriate set of dressed atomic states we show that the emergence of gain is related to the existence of a population inversion between the upper level of the lasing transition and two of the lower lying dressed states.

The Dressed State Picture in Quantum Coherence and Interference

Abstract We investigate the advantageous description of driven multi-level systems in the dressed state representation. A demonstration is given for the cases of subnatural line narrowing and lasing without inversion.