Abstract

We show that lasing without inversion (LWI) can be obtained via a self-pulsing instability [1] in the double-lambda scheme suggested by Kocharovskaya and Mandel [2] with the atomic configuration proposed by Fleischhauer and Scully [3]. Two resonant plane-wave uniform coherent fields, a strong driving field and a probe field, co-propagating in a unidirectional ring laser cavity are considered. The parallel linear polarization between driving and probe fields is investigated as the favourable configuration for obtaining LWI through quantum interference in the absorption profile of the probe field. In addition, as in the scheme proposed by Fleischhauer and Scully, an incoherent field is introduced for optically pumping the population of the lower levels of the probe field transition (mj=±l) into a third sublevel of the ground state (mj=0) We have obtained analytical expressions for tne linear stability analysis of the non-lasing solution, finding explicit necessary conditions for LWI through the well known pitchfork bifurcation, giving rise to cw emission, and through a Hopf bifurcation giving rise to pulsed emission. Each of these bifurcations can be reached only in a limited domain of driving field intensities. These domains are determined analytically as a function of the cavity losses, unsaturated gain, population differences, and coherence relaxation rates. Both bifurcations appear for a good quality cavity but, while pitchfork bifurcation depends on the ratio between cavity losses and gain, the Hopf bifurcation depends separately on these parameters. Moreover, it is shown that by only changing the driving field intensity the system can reach both bifurcations. Points of codimension-2 bifurcations are also found.

© 1996 IEEE