Enhanced index of refraction in four-wave mixing media

TL;DR

This paper predicts and analyzes how four-wave mixing in a four-level atomic system can significantly enhance the refractive index while minimizing absorption, with practical estimates for potassium gases.

Contribution

It provides a detailed analysis of maximal index enhancement in four-level FWM systems and practical estimates for real atomic gases, including effects of broadening and multilevel structures.

Findings

Maximal index enhancement predicted in four-level FWM systems.

Estimated index change for potassium gases considering broadening effects.

Proposed two-species system to achieve vanishing absorption without amplification.

Abstract

Refractive index enhancement accompanied by vanishing absorption in a four-level atomic system interacting with two control and two probe fields in a regime of four-wave mixing (FWM) has been predicted and studied in the present work. We analyzed the maximal index enhancement in the four-level FWM system and gave index estimates for a real atomic gas of $^{40}$K, taking into account its multilevel structure and collisional and Doppler broadenings at large atomic densities. We also discussed how vanishing absorption with no nearby amplification can be realized in a two species system, consisting of a four-level FWM and a two-level system, where the latter provides additional absorption for one of the probe fields. We numerically estimated the index change in a system composed of $^{40}$K and $^{39}$K gases.