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Acta Physica Sinica

ATOMIC COHERENCE INDUCED BY TWO-PHOTON PROCESS——TRANSITION FROM LASING WITH INVERSION TO LASING WITHOUT INVERSION

Xiangming Hu, Wang Dexin, (1)华中师范大学物理系; (2)华中师范大学应用物理研究所

Published Jan 1, 1997• 1 citation
Publisher

Abstract

In this paper, the pumping mechanism in the closed Ξ-type three-level system can be simplified using the coherence induced by the two-photon process. The system exhibits either lasing with inversion or lasing without inversion so long as there exists the pumping field. The system exhibits the transition from lasing with inverson to lasing without inversion under certain conditions. Near the transition lasing without inversion may be as efficient as lasing with inversion.

DOI
10.7498/aps.46.61

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In this paper, the pumping mechanism in the closed Ξ-type three-level system can be simplified using the coherence induced by the two-photon process. The system exhibits either lasing with inversion or lasing without inversion so long as there exists the pumping field. The system exhibits the transition from lasing with inverson to lasing without inversion under certain conditions. Near the transition lasing without inversion may be as efficient as lasing with inversion.
We show lasing without population inversion in a closed four-level atomic system which is no longer incoherently pumped on the transition at which lasing occurs. The four-level system can overcome some limits in the typical lambda-type and V-type three-level systems, furthermore it is possible to achieve lasing even in the absence of the inversion condition for the thermal radiation fields or of the inversion of spontaneous decay rate. We find that when the detuning of probe field is equal to that of coherent coupling field, there is a peak value along with the increase of the detuning. To explain it, we bring forward that there are adiabatic and nonadiabatic stimulated Raman processes when a three-level atomic system is interacted with two coherent fields, so there are two mechanisms influencing the change of probe field. We believe that it can explain more general lasing without inversion processes because of quantum interference induced by coherent fields.
Noninversion lasing is investigated in \ensuremath{\Lambda}-type three-level atomic systems that are coupled to two modes of the electromagnetic field. As a result of an external field driving the transition between the lower two closely spaced levels, laser action can be achieved in both modes simultaneously at arbitrarily small initial upper-level population (lasing without inversion) provided the pumping rate exceeds a certain threshold. The relative phase of the two modes is locked to a particular value controlled by the phase of the external field. In addition, new regimes of the laser operation arise when initial coherences between various atomic levels are also injected into the resonator. Firstly, laser action can be achieved in both modes at arbitrarily small pumping (no threshold). Secondly, the injected atomic coherence can control competition between the modes, and result in a variety of multistable steady-state behavior illustrating the very sensitive dynamics of the system.