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Physical Review A

Phase control of light amplification without inversion in a Λ system with spontaneously generated coherence

Jin‐Hui Wu, Jin-Yue Gao

Published Jun 4, 2002• 123 citations
Publisher

Abstract

Due to interaction with the vacuum of the radiation field, near-degenerate lower levels in a $\ensuremath{\Lambda}$ system have an additional coherence term, the spontaneously generated coherence term. In this paper, we investigate effects of spontaneouly generated coherence on inversionless gain in the presence of a weak probe, a strong coherent field, and an incoherent pump. We find that the inversionless gain stems from both spontaneously generated coherence and dynamically induced coherence, but the former contributes more to the inversionless gain. In particular, we can modulate the inversionless gain just by changing the relative phase between the two fields.

DOI
10.1103/physreva.65.063807

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Due to interaction with the vacuum of the radiation field, near-degenerate lower levels in a \ensuremathΛ\ensuremath{\Lambda}\ensuremathΛ system have an additional coherence term, the spontaneously generated coherence term. In this paper, we investigate effects of spontaneouly generated coherence on inversionless gain in the presence of a weak probe, a strong coherent field, and an incoherent pump. We find that the inversionless gain stems from both spontaneously generated coherence and dynamically induced coherence, but the former contributes more to the inversionless gain. In particular, we can modulate the inversionless gain just by changing the relative phase between the two fields.
Phase Dependence of the Inversionless Gain in a Λ\LambdaΛ System with Near-Degenerate Levels
Due to interaction with the vacuum of the radiation field, near-degenerate lower levels in a $\ensuremath{\Lambda}$ system have an additional coherence term, the spontaneously generated coherence term. In this paper, we investigate the effects of this kind of coherence on the transient process in the presence of a weak probe and a strong coherent field, with or without an incoherent pump. We find that the transient gain (absorption) properties can be dramatically affected by the spontaneously generated coherence. The transient gain can be greatly enhanced due to the effect of spontaneously generated coherence, and the transient absorption can be completely eliminated just by choosing the proper relative phase between the two fields.
The effects of incoherent pumping on the phase control of amplification without inversion (AWI) are investigated in a three-level Λ system with a weak probe field. It is shown that, similar to spontaneously generated coherence, incoherent pumping is necessary to make the system become sensitive to the relative phase. We find that the region in which AWI can be exhibited is widened with the enhancement of incoherent pumping, and that the amplitude of the probe gain can be also changed where there exists an extremum of the amplitude for a given probe detuning.
We investigate the effects of spontaneously generated coherence (SGC) on both the steady and transient gain properties in a four-level inverted-Y-type atomic system in the presence of a weak probe, two strong coherent fields, and an incoherent pump. For the steady process, we find that the inversionless gain mainly origins from SGC. In particular, we can modulate the inversionless gain by changing the relative phase between the two fields. Moreover, the amplitude of the gain peak can be enhanced and the additional gain peak can appear by changing the detuning of the coupling field. As for the transient process, the transient gain properties can also be dramatically affected by the SGC. Compared to the case without SGC, the transient gain can be greatly enhanced with completely eliminated transient absorption by choosing the proper relative phase between the two fields. And the inverted-Y-type system with SGC can be simulated in both atomic and semiconductor quantum well systems avoiding the conditions of SGC.
This paper investigates the control role of the relative phase between the probe and driving fields on the gain, dispersion and populations in an open Λ system with spontaneously generated coherence (SGC). It shows that by adjusting the value of the relative phase, a change from lasing with inversion to lasing without inversion can be realized; the values and frequency spectrum regions of the inversionless gain and dispersion can be obviously varied; high refractive index with zero absorption and electromagnetically induced transparency can be achieved. It is also found that when the driving field is resonant, the shapes of the dispersion and the gain curves versus the probe detuning are very similar if the relative phase of the dispersion lags π/2 than that of the gain, however for the off-resonant driving field the similarity will disappear; the gain, dispersion and populations are periodical functions of the relative phase, the modulation period is always 2π; the contribution of SGC to the inversionless gain and dispersion is much larger than that of the dynamically induced coherence.