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Chinese Physics

Effect of spontaneously generated coherence on inversionless lasing gain in an atomic system with Doppler broadening

Hui Ma, Xia Tan, Shufen Tian, Tong Dian-Min, Fan Xijun

Published Aug 1, 2007• 4 citations
Publisher

Abstract

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.

DOI
10.1088/1009-1963/16/8/041

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In this paper we study influences of Doppler broadening,spontaneously generated coherence,and other system parameters on propagation effect in a quasi lambda-type four-level atomic system.It is shown that when the Doppler broadening is present,generally speaking,the values of gain and intensity of lasing without inversion (i.e.the probe field) in the co-propagating probe and driving fields case are much larger than those in the counter-propagating case;considerably larger gain and intensity of lasing without inversion than those without the Doppler broadening can be obtained by choosing appropriate values of the Doppler broadening width and spontaneously generated coherence strength.The gain and intensity of lasing without inversion increase with the increase of spontaneously generated coherence strength;when spontaneously generated coherence is present,much larger gain and intensity of lasing without inversion than those in the case without spontaneously generated coherence can be obtained.Choosing suitable values of the probe detuning,Rabi frequencies of the driving and pump fields at the entrance of the medium also can remarkably enhance the gain and intensity of lasing without inversion.更多还原

Chinese Physics B•Jan 1, 2012•0 citations
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.
By using the numerical calculation results of the density matrix equations of motion of a closed Λ-type inversionless lasing system,the effects of the propagation of light fields on the gain of lasing without inversion(LWI),Rabi frequencies of the probe and driving fields,and the modulation role of spontaneously generated coherence(SGC) on the effects were investigated when the Doppler broadening presents.It was shown that,with the distance increasing,LWI gain first increases and then decreases,Rabi frequency of the probe field(the driving field) increases monotonously(decreases);at a specific propagation distance,LWI gain first increases and then decreases with increasing of the Rabi frequency of the driving field at the entrance of the medium,and LWI gain decreases monotonously with increasing of the Doppler broadening width;SGC has a remarkable manipulation role on the effect of propagation of the light fields,the LWI gain with SGC is much larger than that without SGC.
The effect of spontaneously generated coherence on the gain of lasing without inversion(LWI) is studied in an open quasi-Λ type four-level atomic system with Doppler broadening from different respects.The results show that,for a fixed SGC strength,LWI gain decreases with increasing the value of the Doppler width;no matter the Doppler broadening is obvious or not,the LWI gain larger than that without SGC always can be gotten by choosing suitable value of the SGC strength,and this difference becomes more evident with the Doppler width decreasing;the atomic exit and injection rates also can dramatically affect LWI gain;a much larger LWI gain in open system than that in the corresponding closed system can be obained.
We studied the controlling role played by the relative phase between the probe and driving fields on inversionless gain of the probe field in a closed and Doppler broadened Λ-type three-level system with spontaneously generated coherence (SGC). It was found that：(1) Regardless of the driving field being in or off resonance, and regardless of the probe and driving fields being co- or counter- propagating, the gain maximum value always varies periodically with variation of the relative phase with the period 2π. (2) When the driving field is in resonance, the gain maximum value decreases monotonicly with Doppler width increasing, and moreover, the decreasing in the counter-propagation case is faster than that in the co-propagation case. When the driving field is off resonance, the gain maximum value does not monotonicly decrease or increase with Doppler width increasing. In both above cases, the largest inversionless gain can be gotten by adjusting the relative phase. (3) The contribution of SGC to the inversionless gain is much larger than that of the dynamically induced coherence.
In this paper we study influences of Doppler broadening, spontaneously generated coherence, and other system parameters on propagation effect in a quasi lambda-type four-level atomic system. It is shown that when the Doppler broadening is present, generally speaking, the values of gain and intensity of lasing without inversion (i.e. the probe field) in the co-propagating probe and driving fields case are much larger than those in the counter-propagating case; considerably larger gain and intensity of lasing without inversion than those without the Doppler broadening can be obtained by choosing appropriate values of the Doppler broadening width and spontaneously generated coherence strength. The gain and intensity of lasing without inversion increase with the increase of spontaneously generated coherence strength; when spontaneously generated coherence is present, much larger gain and intensity of lasing without inversion than those in the case without spontaneously generated coherence can be obtained. Choosing suitable values of the probe detuning, Rabi frequencies of the driving and pump fields at the entrance of the medium also can remarkably enhance the gain and intensity of lasing without inversion.
In this paper we study the influence of spontaneously generated coherence (SGC) on propagation effect and the modulation role of the atomic exit rate(r0)and ratio(S) of the atomic injection rates on the SGC-dependent propagation effect in an open V-type three-level lasing without inversion(LWI) system with Doppler broadening,by using the calculation results of the density matrix motion equations and the propagation equations of the driving and probe fields,in order to get larger LWI gain and intensity of the probe field.It is shown that with propagation distance increasing,LWI gain and Rabi frequency(intensity) of the probe field first increase and then decrease,while the Rabi frequency(intensity) of the driving field decreases monotonously;LWI gain and Rabi frequency(intensity) of the probe field increase with SGC strength(measured by θ) increasing.When θ=π,we can obtain the largest LWI gain and Rabi frequency(intensity) of the probe field;in the case with SGC,we can get much larger LWI gain and Rabi frequency(intensity) of the probe field than those in the case without SGC.In certain value ranges of r0 and S,LWI gain and Rabi frequency(intensity) of the probe field increase with r0 and S increasing.By choosing proper values of γ0 and S,in the open system we can obtain much higher LWI gain and Rabi frequency(intensity) of the probe field than those in the corresponding closed system.
In this paper we study influences of Doppler broadening,spontaneously generated coherence,and other system parameters on propagation effect in a quasi lambda-type four-level atomic system.It is shown that when the Doppler broadening is present,generally speaking,the values of gain and intensity of lasing without inversion (i.e.the probe field) in the co-propagating probe and driving fields case are much larger than those in the counter-propagating case;considerably larger gain and intensity of lasing without inversion than those without the Doppler broadening can be obtained by choosing appropriate values of the Doppler broadening width and spontaneously generated coherence strength.The gain and intensity of lasing without inversion increase with the increase of spontaneously generated coherence strength;when spontaneously generated coherence is present,much larger gain and intensity of lasing without inversion than those in the case without spontaneously generated coherence can be obtained.Choosing suitable values of the probe detuning,Rabi frequencies of the driving and pump fields at the entrance of the medium also can remarkably enhance the gain and intensity of lasing without inversion.更多还原