Index of refraction engineering in five level DIGS atoms

TL;DR

This paper proposes a five-level atomic system in rubidium vapors that can significantly enhance or reduce the index of refraction with minimal absorption, enabling advanced control of light propagation.

Contribution

It introduces a novel five-level atomic scheme allowing large, tunable index of refraction modifications with vanishing absorption, surpassing previous proposals in magnitude.

Findings

Index of refraction up to approximately 1.2×10^{-14}N in rubidium vapors.

Ability to switch the index below 1 by changing field detunings.

Robustness of the index enhancement against broadening effects.

Abstract

We present a five level atomic system in which the index of refraction of a probe laser can be enhanced or reduced below unity with vanishing absorption in the region between pairs of absorption and gain lines formed by dressing of the atoms with a control laser and RF/microwave fields. By weak incoherent pumping of population into a single metastable state, one can create several narrow amplifying resonances. At frequencies between these gain lines and additional absorption lines, there exist regions of vanishing absorption but resonantly enhanced index of refraction. In $Rb$ vapors with density $N$ in units of $cm^{-3}$, we predict an index of refraction up to $n \approx \sqrt{1+1.2\times10^{-14}N}$ for the D1 line, which is more than an order of magnitude larger than other proposals for index of refraction enhancement. Furthermore, the index can be readily reduced below 1 by simply changing the sign of the probe or RF field detunings. This enhancement is robust with respect to homogeneous and inhomogeneous broadening.