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Effect of vacuum-induced coherence on lasing without inversion in an equispaced three-level ladder system

Jun Qian, 刘呈普, 龚尚庆

Published Jan 1, 2005• 0 citations
OpenAlex

Abstract

The effects of vacuum-induced coherence (VIC) on the properties of the absorption and gain of the probe field in an equispaced three-level ladder atomic system are investigated. It is found that lasing without inversion (LWI) is remarkably enhanced due to the effect of VIC in the case of the small incoherent pump rate.

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Journal of Physics B Atomic Molecular and Optical Physics•Mar 1, 2006•20 citations
We find that in the open and closed ladder systems with vacuum induced coherence, the relative phase between the probe and driving fields has an important manipulation role on the absorption property, while the incoherent pumping has a considerable effect on the phase-dependent absorption property.In the both systems, by adjusting the incoherent pumping the switching from absorption to gain and from lasing with inversion to lasing without inversion (LWI) can be realized and the largest LWI gain can be gotten.However, when the incoherent pumping is absent, for any value of the relative phase, LWI still can't be obtained in the closed system but can in the open system; moreover, in the open system, for suitable values of the relative phase, LWI gain gotten when the incoherent pumping is absent is obviously larger than that obtained when the incoherent pumping presents.
In the open and closed ladder systems with vacuum induced coherence,it is found that the relative phase between the probe and driving fields has an important manipulation role on the absorption property,while the incoherent pumping has a considerable effect on the phase-dependent absorption property.In both systems,by adjusting the incoherent pumping the switching from absorption to gain and from lasing with inversion to lasing without inversion can be realized and the largest inversionless gain can be gotten.However,when the incoherent pumping is absent,for any value of the relative phase,lasing without inversion still can not be obtained in the closed system but it is able in the open system;and in the open system,for suitable values of the relative phase,inversionless gain gotten when the incoherent pumping is absent is obviously larger than that obtained when the incoherent pumping presents.
When the interactions of the two coupling transitions from an excited level to two nearly degenerate ground levels with the same vacuum occur in a four-level tripod-scheme atomic system, vacuum-induced coherence (VIC) results from the quantum interference between the two spontaneous transitions. We investigate the effects of VIC and the relative phase between the two coupling fields on the probe absorption and dispersion properties as well as the group velocity of the probe field. We find that by adjusting the incoherent pumping field and VIC as well as the relative phase, the central absorption peak in the double transparency spectrum reduces, even develops into a gain dip, and the probe field propagates at a velocity from superluminal to subluminal. It is particularly pointed out that the subluminal light propagation with gain without inversion can be realized in such a system. The physical interpretation of the phenomena has been given.
In a three-level V-type atomic system without any external coherent driving, owing to the coherence that results from the vacuum of the radiation field, both the probe gain with and without population inversion can be achieved with very weak incoherent pumping. The gain is achieved in the absence of any external coherent driving field, so it is different from the gain without inversion in ordinary laser-driven schemes where a coherent driving field is necessary to create the coherence. The gain is also different from the conventional lasing gain because the population inversion is achieved via vacuum-induced coherence, which is dependent on the atomic coherence.