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Physica Scripta

High refractive index without absorption via spontaneously generated coherence in a three-level ladder system

Sulagna Dutta

Published Jun 14, 2010• 6 citations
Publisher

Abstract

A large refractive index without absorption in a closed three-level ladder system with incoherent pumping in the presence of spontaneously generated coherence (SGC) is investigated. It has been found that a large refractive index without absorption can be obtained by choosing proper system parameters. The maximum value of refractive index at vanishing absorption depends on the strength of the SGC parameter.

DOI
10.1088/0031-8949/82/01/015402

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A large refractive index without absorption in a closed three-level ladder system with incoherent pumping in the presence of spontaneously generated coherence (SGC) is investigated. It has been found that a large refractive index without absorption can be obtained by choosing proper system parameters. The maximum value of refractive index at vanishing absorption depends on the strength of the SGC parameter.
We studied a closed three-level V-type system with two near-degenerate excited levels in the presence of an incoherent pumping field. Quantum interferences of the two-decay channels lead to the achievement of the high index of refraction without absorption via spontaneously generated coherence. We use the exact analytical formula of the refractive index derived by us in a recent paper. We found that the high refractive index varies very much with the angle between the two dipole moments and evidently with the detuning of the coupling field.
The probe response and dispersion of a three-level closed ? system considering spontaneously generated coherence (SGC) have been investigated with and without an incoherent pumping. One can get electromagnetically induced transparency (EIT) whatever be the value of the SGC parameter and phase difference when an incoherent pump is absent. But by turning the incoherent pump rate on, one can control the light propagation from subluminal to superluminal and also the nonlinear response from EIT to electromagnetically induced absorption (EIA) by controlling the SGC parameter and phase difference. Using the incoherent pump rate as an optical tool, the desired configuration around the resonance can be realized. Exact analytical expressions for the coherences in the steady-state limit have been derived in the absence of an incoherent pump rate (keeping all orders of the system parameters) to generalize the analysis, and any restriction on the system parameters has been avoided to make it applicable to various atomic and molecular systems.
The effect of spontaneously generated coherence （SGC） on transient evolution of gain of lasing without inversion （LWI） and modulation roles of the injection rate ratio and exit rate on SGC-dependent gain in an open Ladder type three level system are studied by using the numerical solution of the density matrix motion equation of the system. It was shown that: variation of SGC strength will make the transient and final stationary gains having a considerable changing; when incoherent pumping presents, LWI gain increases with the ratio of injection rates and exit rate decreasing, however, when incoherent pumping is absent, the case is just the opposite; by choosing suitable values of SGC strength, the injection rate ratio and exit rate, we can obtain the largest transient and final stationary gain.
The effects of spontaneously generated coherence (SGC) on the propagation of a weak probe pulse are investigated in a ladder-type atomic system. Due to SGC, the properties of the dispersion and the absorption of a three-level ladder-type system are changed greatly. With proper parameters, the system can produce normal and anomalous dispersion regions in the gain region. The effects of the incoherent pumping and the relative phase on the group velocity are also studied. They all can be used as switches to manipulate the group velocity of the weak probe field from gain-assisted sub- to superluminance.
We propose a scheme for realizing negative refractive index in a multilevel atomic system. The theoretical modeling has been done using density matrix approach in which the spontaneously generated coherence (SGC) is also induced. It is shown that the negative refractive index can be obtained on the effect of quantum coherence. The parameters () quantifying left-handedness in the system become more negative if the SGC is defined in the appropriate value. Furthermore, left-handed material with reduced absorption is possible by choosing appropriate parameters.