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Journal of Foshan University

Effects of spontaneously generated coherence on lasing without inversion in a ladder-type three-level atomic system

Cen Jing-sheng

Published Jan 1, 2010• 0 citations
OpenAlex

Abstract

An investigation into lasing without inversion in a Ladder-type three-level atomic system was conducted.With the exhibiting condition of lasing without inversion,the effects of the incoherent pumping and spontaneously generated coherence(SGC) have been studied in detail.The investigation shows that SGC can decrease the phenomena of lasing without inversion(LWI).However,the incoherent pumping can strengthen it.

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An investigation into lasing without inversion in a Ladder-type three-level atomic system was conducted.With the exhibiting condition of lasing without inversion,the effects of the incoherent pumping and spontaneously generated coherence(SGC) have been studied in detail.The investigation shows that SGC can decrease the phenomena of lasing without inversion(LWI).However,the incoherent pumping can strengthen it.
We have studied the effect of the spontaneously generated coherence (SGC) on gain of lasing without inversion (LWI) in a closed three-level Λ-type atomic system with Doppler broadening. It is shown that, regardless of the driving and probe fields being co- or counter-propagating, at a suitable value of the Doppler width, we can obtain a much larger LWI gain with SGC than that without SGC; and the region of the LWI gain spectrum with SGC is obviously larger than that without SGC. When the Doppler width takes a constant value, the gain does not monotonically decrease or increase with increasing strength of SGC, the largest LWI gain can be obtained by adjusting strength of SGC. Generally speaking, the co-propagating probe and driving fields is favourable to obtain a larger LWI gain.
We put forward a model of an open quasi Λ-type four-level atomic system,and then investigate the effect of spontaneously generated coherence(SGC) on the gain of lasing without inversion from different respects by using the numerical calculation results of the system in the steady state.The study results show that,the switching from absorption to lasing without inversion(LWI) and the enhancement of the LWI gain can be realized by adjusting the strength of SGC;the variety of the two factors p1 to p2 which represent the SGC effect will produce remarkable different influence on the LWI gain.We also find that,the LWI gain is much larger in open system than that in the corresponding closed system;moreover,when the incoherent pump field is absent,the LWI gain can be obtained in the open system but cant in the closed system.
The effect of spontaneously generated coherence （SGC） on transient evolution of gain of lasing without inversion （LWI） and modulation roles of the injection rate ratio and exit rate on SGC-dependent gain in an open Ladder type three level system are studied by using the numerical solution of the density matrix motion equation of the system. It was shown that: variation of SGC strength will make the transient and final stationary gains having a considerable changing; when incoherent pumping presents, LWI gain increases with the ratio of injection rates and exit rate decreasing, however, when incoherent pumping is absent, the case is just the opposite; by choosing suitable values of SGC strength, the injection rate ratio and exit rate, we can obtain the largest transient and final stationary gain.
In this paper, we investigate the effects of spontaneously generated coherence (SGC) on the conditions for exhibiting lasing without inversion (LWI) in the presence of a weak probe and a strong-coupling field. We find that owing to the effect of SGC, LWI can be realized without the incoherent pumping or the decay between two upper levels. However, in the region where LWI can be exhibited, the effect of SGC term on the exhibition of LWI is not always positive, sometimes it can even cumber the realization of LWI for some values of SGC. These values are given in this paper. In addition, we also analyze the essence of the generation of the probe field.