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ABSORPTION-FREE SUPERLUMINAL LIGHT PROPAGATION IN A V-TYPE SYSTEM

S. W. Rabiei, Kh. Saaidi, B. Ruzbahani, Mohammad Mahmoudi

Published Jan 18, 2010• 1 citation
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Abstract

Physics Department, Zanjan University, P. O. Box 45195-313, Zanjan, Iran(Dated: May 20, 2010)Dispersion and absorption properties of a weak probe field in a three-level V-type atomic systemis studied. By application of indirect incoherent pump fields the effect of populating upper levels onoptical properties of the atomic medium in presence of a strong coherent pump field is investigated.It is shown that the slope of dispersion switches from positive to negative just by changing theintensity of the coherent or indirect incoherent pump fields. It is demonstrated that the absorption-free superluminal and subluminal light propagation appear in this system.

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Physics Department, Zanjan University, P. O. Box 45195-313, Zanjan, Iran(Dated: May 20, 2010)Dispersion and absorption properties of a weak probe field in a three-level V-type atomic systemis studied. By application of indirect incoherent pump fields the effect of populating upper levels onoptical properties of the atomic medium in presence of a strong coherent pump field is investigated.It is shown that the slope of dispersion switches from positive to negative just by changing theintensity of the coherent or indirect incoherent pump fields. It is demonstrated that the absorption-free superluminal and subluminal light propagation appear in this system.
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.
We study the change of the probe field group velocity from subluminal to superluminal range for two kinds of closed three-level V-type system with spontaneously generated coherence and incoherent pumping field. For the first kind of the V-type system we deduce the analytical formula of the group velocity, while for the second kind of the V-type system we solve numerically the density matrix equations system and apply it to a real system from the LiH molecule. We find that the group index of the probe field can be changed from positive to negative within the appropriate choice of the relative phase between the probe and coupling field phases, the incoherent pumping rate and probe detuning.
We study the influence of the angle between the two dipole transition moments on the group velocity for two kinds of three-level V-type systems with spontaneously generated coherence and incoherent pumping. The group velocity of the probe field for both kinds of the V-type systems alternates between the subluminal or superluminal regimen. We can choose a real three-level V-type system from atoms or molecules to exhibit subluminal or superluminal light propagation by a proper geometry of the probe, coupling and incoherent pumping fields, which depends on the angle between the two dipole transition moments.
The propagation of a weak probe field in a four-level N-type quantum system in the presence of spontaneously generated coherence (SGC) is theoretically investigated. The optical properties of the system are studied and it is shown that the group velocity of light pulse can be controlled by relative phase of applied fields. By changing the relative phase of applied fields, the group velocity of light pulse changes from transparent subluminal to the transparent superluminal light propagation. Thus, the phase-controlled absorption-free superluminal light propagation is obtained without applying an incoherent laser fields to the system. The propagation of a weak probe light pulse is studied by solving the Maxwell's wave equation on numerical grid in space and time. Moreover, we study the third order self- and cross-Kerr susceptibility of probe field and calculate the nonlinear cross-phase shift for different values of intensity of applied fields. In addition, we take into account the effect of Doppler broadening on the light pulse propagation and it is found that a suitable choice of laser propagation directions allows us to preserve our results even in the presence of Doppler effect. It is demonstrated that by increasing the Doppler width of distribution to the room temperature, the dispersion changes from transparent subluminal to transparent superluminal light propagation which is our major motivation for this work.