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Physica Scripta

Analysis of light propagation in an anomalously dispersive medium

P A Grochowska, Sylwia Zielińska‐Raczyńska

Published Apr 1, 2014• 1 citation
Publisher

Abstract

We analyse the propagation of a probe laser pulse though a medium of atoms in the double Λ configuration with two closely spaced upper levels. The medium is irradiated with a strong coherent field and is additionally incoherently pumped. Depending on the parameters of the system the dispersion of the medium may change alternatively from normal to anomalous with absorption varying from positive to negative (gain). The incoherent optical pump was found to be the switch between the sub- and the superluminal regime. A laser field propagating through such an optical system can experience alternatively the negative or positive group velocity. The dynamics of propagation in the case of positive but larger than c group velocities is investigated in particular. In this paper we show how the description in terms of the group velocity breaks down in the superluminal regime.

DOI
10.1088/0031-8949/2014/t160/014015

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We analyse the propagation of a probe laser pulse though a medium of atoms in the double Λ configuration with two closely spaced upper levels. The medium is irradiated with a strong coherent field and is additionally incoherently pumped. Depending on the parameters of the system the dispersion of the medium may change alternatively from normal to anomalous with absorption varying from positive to negative (gain). The incoherent optical pump was found to be the switch between the sub- and the superluminal regime. A laser field propagating through such an optical system can experience alternatively the negative or positive group velocity. The dynamics of propagation in the case of positive but larger than c group velocities is investigated in particular. In this paper we show how the description in terms of the group velocity breaks down in the superluminal regime.
We analyse the group velocity of a laser pulse in an optically dressed atomic system. A Λ system with an additional close upper level and an incoherent pump is specially investigated. The group velocity of a pulse is strongly dependent on the optical properties of the system which can be modified by changing the amplitude or detuning of a strong coupling field or of an incoherent pump between the two lower levels of the system. Depending on the parameters, the medium may have alternatively absorptive or gain properties and the dispersion can be changed from anomalous into a normal one. The ranges of parameters are especially investigated in which absorption (gain) is not too strong, with dispersion being not too steep. The group velocity of a pulse propagating through a sample with such optical properties can be switched from the subinto superluminal regime. The dynamics of propagation in the case of negative group velocities of a small absolute value is especially interesting. In such a regime the peak of the transmitted pulse exits the sample before the peak of the incoming pulse reaches the medium. The transmitted pulse splits into two pulses - one of them propagates forward behind the medium and the other propagates backward and is cancelled at the entrance of the sample by the incoming pulse. Ranges of parameters are seeked in which the shape of the pulse is changed and the group velocity as a single parameter is not sufficient to describe the pulse propagation.
Abstract Light-matter interaction between a light field and an atomic medium could be used to manipulate the medium’s dispersive properties, leading to subluminal and superluminal regimes. Utilizing the same idea, this work investigates the propagation of structured superluminal light and anomalous phase shifts in a Λ- type three-level atomic medium, where a structured control field governs the atomic system. The absorption and dispersion properties are modulated by the azimuthal quantum number (ℓ) of the control field. The maxima and minima of the absorption spectrum, along with the corresponding normal and anomalous dispersion peaks, are enhanced with a (2ℓ) dependence on the azimuthal quantum number in the medium. The negative group index and anomalous phase shift vary within the ranges −1000 ≤ ng ≤ −900 and −6.5 × 10 5 ≤ ϕ ≤ −5.6 × 10 5 rad, respectively. The corresponding group velocity lies in the range −3.33 × 10 5 ≤ vg ≤ −3.0 × 10 5 m/s within the spatial region −2λ ≤ x, y ≤ 2λ. Furthermore, the anomalous phase shift is significantly enhanced in regions exhibiting superluminal behavior, following the (2ℓ) azimuthal quantum number dependence. The findings of this work may have potential applications in optical storage devices, imaging, coding, and the design of advanced photonic technologies.
Abstract The manipulation of the group velocity of light is very important in further information processing and quantum network. It is well known that subluminal and superluminal light propagation can be obtained by controlling the dispersion property of the experimental medium. In order to realize the switching from normal dispersion to anomalous dispersion at the same frequency, we investigate the dispersion and absorption properties of a four-level atomic system. By adjusting the intensity of an incoherent pump, we get transparent normal dispersion and lossless anomalous dispersion, which lead to subluminal and superluminal light propagation respectively. For a strong incoherent pump, the intensity of the coherent coupling field also can be used to realize a similar switching effect.
Dispersion and absorption properties of a weak probe field in a three-level V-type atomic system is studied. By application of indirect incoherent pump fields the effect of populating upper levels on optical properties of the atomic medium in presence of a strong coherent pump field is investigated. It is shown that the slope of dispersion changes from positive to negative just by changing the intensity of the coherent or indirect incoherent pump fields. It is demonstrated that the absorption-free subluminal and superluminal light propagation appears in this system.