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Journal of Physics B Atomic Molecular and Optical Physics

Realization of a negative refractive index in a three-level Λ system via spontaneously generated coherence

Sulagna Dutta, Krishna Rai Dastidar

Published Oct 19, 2010• 15 citations
Publisher

Abstract

A new scheme to realize simultaneous negative permittivity and permeability in a three-level closed Λ system with incoherent pumping via spontaneously generated coherence has been presented. We have shown that the negative refractive index can be realized in a heteronuclear molecule such as LiH. The negative refractive index can be achieved in a band of frequency range. The position and the band of the frequency region of negative refraction can be manipulated by controlling the incoherent pump rate. We achieve a figure of merit (FOM) = |Re( n )/Im( n )| = 1.797 for the LiH molecule.

DOI
10.1088/0953-4075/43/21/215503

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A new scheme to realize simultaneous negative permittivity and permeability in a three-level closed Λ system with incoherent pumping via spontaneously generated coherence has been presented. We have shown that the negative refractive index can be realized in a heteronuclear molecule such as LiH. The negative refractive index can be achieved in a band of frequency range. The position and the band of the frequency region of negative refraction can be manipulated by controlling the incoherent pump rate. We achieve a figure of merit (FOM) = |Re( n )/Im( n )| = 1.797 for the LiH molecule.
A new approach is suggested to realize simultaneous negative permittivity and permeability in a three level closed system with incoherent pumping via spontaneously generated coherence (SGC). In this system the negativity of the real part of magnetic permeability can be achieved in the presence of SGC whereas in the absence of SGC it is positive. Thus the SGC makes the system a negative index medium (NIM) in a band of frequency range. The position and the band of the frequency region of negative refraction can be manipulated by controlling the incoherent pump rate. We achieve FOM = 7.91165. We have studied the group index in the negative refractive index region and have shown that the group velocity switches from superluminal to subluminal mode in this region of negative refraction. We have shown that the negative refractive index can be realized in a heteronuclear molecule.
The interplay between dynamically induced coherence (DIC) and spontaneously generated coherence (SGC) can induce electromagnetically induced transparency (EIT) in a three-level closed Λ system. When the contributions from these two coherences are equal in magnitude and opposite in sign at the resonances of both the coherent and probe fields, transparency of the probe light occurs at the resonance with absorption humps away from the resonance. We have demonstrated here that the broadening of the EIT window can be controlled by changing the strength of incoherent pumping. This is a new approach for achieving wide EIT window for lossless and distortionless transmission of light of large spectral width. The most attractive feature of this new method is that the FWHM (full width at half-maximum) of the EIT window is further increased when the broadening due to homogeneous/inhomogeneous decay is taken into consideration. This scheme can be applied in atoms/molecules where SGC can be invoked by dressing two closely spaced levels ( e.g. hyperfine levels in atoms or rovibrational levels in molecules) by an external field. This effect has been demonstrated in a heteronuclear molecule ( e.g. LiH) and examined the role of incoherent pumping for controlling the width of the EIT window in the presence and absence of homogeneous/inhomogeneous decay. The experimental realization of the widening of the EIT window in molecules has been discussed.
Multicolor manipulation of negative refraction in a three-level Λ atomic system is theoretically investigated.Based on multicolor coherence, the negative refractive index can be obtained with reduced absorption.The refractive index can also be controlled by changing the sum of the phases of the sidebands in the trichromatic driving fields.By adjusting the sum phase, the refractive index can be varied between negative and positive in two different frequency bands.Furthermore, the frequency band corresponding to the negative refractive index is widened by increasing the intensity and the frequency difference of the trichromatic field.