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Journal of University of South China

The Change of Group Velocity:from Subluminal to Superluminal Light Propagation in the V System

Zhihua Peng

Published Jan 1, 2009• 0 citations
OpenAlex

Abstract

This paper reveals that the group velocity of a weak laser probe field can be manipulated by controlling the intensity of the driving field applied to a near-degenerate closed three-level V system.Such control can even cause the probe propagation to change from subluminal to superluminal.And the results mentioned above can be understood in terms of dressed states.

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Journal of the Optical Society of America B•May 14, 2015•5 citations
This paper reveals that the group velocity of a weak laser probe field can be manipulated by controlling the intensity of the driving field applied to a near-degenerate closed three-level V system.Such control can even cause the probe propagation to change from subluminal to superluminal.And the results mentioned above can be understood in terms of dressed states.
We show that the group velocity of a weak pulse can be manipulated by controlling the phases of two weak optical fields applied to a V-shaped three-level system. Such control can even cause the probe propagation to change from subluminal to superluminal. We consider two schemes: in the first, the excited states are coupled by decay-induced coherence, which is an inherent property of the medium, and in the second, quantum coherence is created by coupling the excited states to each other by a strong microwave field. We also discuss the group velocity reduction experienced by a single weak propagating probe due to decay-induced coherence.
A four-level atomic system interacting with two strong drive fields and a weak probe field has been studied. We demonstrate that the group velocity of probe field can be controlled to switch from subluminal to superluminal or even negative values around the probe resonance without any significant absorption. The basic idea is to create a gain with slow light on the probe beam resonance with one drive field while the other drive creates a dip in the gain profile of probe leading to superluminal and negative group velocities. A simple switching from slow light to negative group velocity light can be obtained by changing the relative intensities of drive fields. We also describe a control to tune the position of slow light frequency continuously simply by adjusting the relative intensities of both the driving fields.
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.