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Lossless Negative Refraction in An Active Dense Gas of Atoms

Peter P. Orth, Jörg Evers, Christoph H. Keitel

Published Nov 2, 2007• 1 citation
OpenAlex

Abstract

Current designs for negative index materials are passive, such that they suffer from significant losses that prohibit applications, in particular towards optical frequencies. We predict, based on nonlinear optical Bloch equations, negative refraction with zero absorption in an active, i.e., amplifying, dense gas of atoms. External laser fields are used to tune the medium's electromagnetic response and an additional weak pumping field controls its absorption properties. Metastable Neon is identified as a suitable experimental candidate at infrared frequencies to implement a lossless active negative index material.

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Current designs for negative index materials are passive, such that they suffer from significant losses that prohibit applications, in particular towards optical frequencies. We predict, based on nonlinear optical Bloch equations, negative refraction with zero absorption in an active, i.e., amplifying, dense gas of atoms. External laser fields are used to tune the medium's electromagnetic response and an additional weak pumping field controls its absorption properties. Metastable Neon is identified as a suitable experimental candidate at infrared frequencies to implement a lossless active negative index material.
The applications of negative index materials (NIM) are currently severely limited by absorption. Subsequent to improvements of metamaterial design, it has been suggested that dense gases of atoms could form NIM with negligible loss. In such gases, the low absorption is facilitated by quantum interference. In this paper, we show that additional gain mechanisms can be used to tune and effectively remove absorption in a dense gas NIM. In our setup, the atoms are coherently prepared by control laser fields, and further driven by a weak incoherent pump field to induce gain. We employ nonlinear optical Bloch equations to analyze the optical response. Metastable neon was identified as a suitable experimental candidate at infrared frequencies to implement a lossless active negative index material.
A new scheme for overcoming losses with incoherent optical gain in a quantum-coherent left-handed atomic vapor is suggested. In order to obtain low-loss, lossless or active left-handed media (LHM), a pump fleld, which aims at realizing population inversion of atomic levels, is introduced into a four-level atomic system. Both analytical and numerical results are given to illustrate that such an atomic vapor can exhibit intriguing electric and magnetic responses required for achieving simultaneously negative permittivity and permeability (and hence a gain-assisted quantum-coherent negative refractive index would emerge). The quantum-coherent left-handed atomic vapor presented here could have four fascinating characteristics: i) three-dimensionally isotropic negative refractive index, ii) double- negative atomic medium at visible and infrared wavelengths, iii) high-gain optical ampliflcation, and iv) tunable negative refractive index based on quantum coherent control. Such a three-dimensionally isotropic gain medium with negative refractive index at visible and infrared frequencies would have a potential application in design of new quantum optical and photonic devices, including superlenses for perfect imaging and subwavelength focusing.
We propose two dense gas schemes of four-level 'Lambda'-type and V-type atoms based on the effect of quantum coherence. It is shown that under certain conditions the dense gas can simultaneously exhibit negative permittivity and negative permeability, and thus become a negative refractive-index material. Furthermore, by analyzing the absorption property of the left-handed materials, we find that the absoption can be reduced via choosing appropriate parameters. Such schemes might be used to fabricate isotropic and homogeneous left-handed material with vanishing absorption in a wider optical frequency band.