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Quantum Electronics

Anomalous dispersion properties of an atomic medium with a closed excitation contour

К. А. Баранцев, A. N. Litvinov, Georgy A. Kazakov, Yu. Rozhdestvensky

Published Jul 31, 2012• 10 citations
Publisher

Abstract

This paper examines the refractive index dispersion in an atomic medium with a closed excitation contour. The refractive index as a function of the algebraic sum of the phases of excitation fields (Φ) and Rabi frequencies is shown to have a maximum for Φ ≤ π/4. A frequency range is found near the maximum where an increase in refractive index is accompanied by amplification of one of the optical fields.

DOI
10.1070/qe2012v042n07abeh014874

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It is interesting to observe that all optical materials with a positive refractive index have a value of index that is of order unity.Surprisingly, though, a deep understanding of the mechanisms that lead to this universal behavior seems to be lacking.Moreover, this observation is difficult to reconcile with the fact that a single isolated atom is known to have a giant optical response, as characterized by a resonant scattering cross section that far exceeds its physical size.Here, we theoretically and numerically investigate the evolution of the optical properties of an ensemble of ideal atoms as a function of density, starting from the dilute gas limit, including the effects of multiple scattering and near-field interactions.Interestingly, despite the giant response of an isolated atom, we find that the maximum index does not indefinitely grow with increasing density but rather reaches a limiting value of n ≈ 1.7.This limit arises purely from electrodynamics, as it occurs at densities far below those where chemical processes become important.We propose an explanation based upon strong-disorder renormalization group theory, in which the nearfield interaction combined with random atomic positions results in an inhomogeneous broadening of atomic resonance frequencies.This mechanism ensures that, regardless of the physical atomic density, light at any given frequency only interacts with at most a few near-resonant atoms per cubic wavelength, thus limiting the maximum index attainable.Our work is a promising first step to understand the limits of the refractive index from a bottom-up, atomic physics perspective, and it also introduces the renormalization group as a powerful tool to understand the generally complex problem of multiple scattering of light overall.

arXiv:2006.01680•Physical Review X•Feb 9, 2021•52 citations
This paper examines the refractive index dispersion in an atomic medium with a closed excitation contour. The refractive index as a function of the algebraic sum of the phases of excitation fields (Φ) and Rabi frequencies is shown to have a maximum for Φ ≤ π/4. A frequency range is found near the maximum where an increase in refractive index is accompanied by amplification of one of the optical fields.
A closed contour of excitation (Δ-scheme) of a three-level atom in an optically dense medium under the action of two optical fields and a microwave field has been studied. It is found that phase relations between exciting fields in this medium play a determining role. It is established that, under certain conditions, in an optically dense Δ-atom medium exhibits a quasi-periodic dependence of the refractive index on the coordinate. The conditions under which this dependence is most pronounced are determined.
It is interesting to observe that all optical materials with a positive refractive index have a value of index that is of order unity. Surprisingly, though, a deep understanding of the mechanisms that lead to this universal behavior seems to be lacking. Moreover, this observation is difficult to reconcile with the fact that a single isolated atom is known to have a giant optical response, as characterized by a resonant scattering cross section that far exceeds its physical size. Here, we theoretically and numerically investigate the evolution of the optical properties of an ensemble of ideal atoms as a function of density, starting from the dilute gas limit, including the effects of multiple scattering and near-field interactions. Interestingly, despite the giant response of an isolated atom, we find that the maximum index does not indefinitely grow with increasing density but rather reaches a limiting value of n ≈ 1.7. This limit arises purely from electrodynamics, as it occurs at densities far below those where chemical processes become important. We propose an explanation based upon strong-disorder renormalization group theory, in which the near-field interaction combined with random atomic positions results in an inhomogeneous broadening of atomic resonance frequencies. This mechanism ensures that, regardless of the physical atomic density, light at any given frequency only interacts with at most a few near-resonant atoms per cubic wavelength, thus limiting the maximum index attainable. Our work is a promising first step to understand the limits of the refractive index from a bottom-up, atomic physics perspective, and it also introduces the renormalization group as a powerful tool to understand the generally complex problem of multiple scattering of light overall.
It is interesting to observe that all optical materials with a positive refractive index have a value of index that is of order unity.Surprisingly, though, a deep understanding of the mechanisms that lead to this universal behavior seems to be lacking.Moreover, this observation is difficult to reconcile with the fact that a single isolated atom is known to have a giant optical response, as characterized by a resonant scattering cross section that far exceeds its physical size.Here, we theoretically and numerically investigate the evolution of the optical properties of an ensemble of ideal atoms as a function of density, starting from the dilute gas limit, including the effects of multiple scattering and near-field interactions.Interestingly, despite the giant response of an isolated atom, we find that the maximum index does not indefinitely grow with increasing density but rather reaches a limiting value of n ≈ 1.7.This limit arises purely from electrodynamics, as it occurs at densities far below those where chemical processes become important.We propose an explanation based upon strong-disorder renormalization group theory, in which the nearfield interaction combined with random atomic positions results in an inhomogeneous broadening of atomic resonance frequencies.This mechanism ensures that, regardless of the physical atomic density, light at any given frequency only interacts with at most a few near-resonant atoms per cubic wavelength, thus limiting the maximum index attainable.Our work is a promising first step to understand the limits of the refractive index from a bottom-up, atomic physics perspective, and it also introduces the renormalization group as a powerful tool to understand the generally complex problem of multiple scattering of light overall.