Limits and possibilities of refractive index in atomic systems

TL;DR

This paper reviews the limits of enhancing the refractive index in atomic systems, highlighting the role of wave mixing and transition frequencies in overcoming traditional constraints.

Contribution

It introduces a novel perspective on increasing the refractive index by utilizing wave mixing and transition frequency tuning in atomic systems.

Findings

Two-level transitions do not significantly enhance the index at fixed density.

Wave mixing offers a potential method to surpass traditional index limits.

Transition frequencies are key parameters influencing the attainable refractive index.

Abstract

Manipulation of the refractive index has been of growing interest lately. We consider parameters and possibilities of enhancing the absolute-value limit of the linear index in coherent atomic systems. Starting with a review of how two-level transitions - without and with added coherence effects - do not realistically allow for a significantly enhanced index at fixed atomic density, we discuss a possible way around this using wave mixing. This confirms that the only parameters, besides the medium optical depth/density, that can effectively change the value of the attainable index are the frequencies of the involved transitions.