Abstract

A four level `N-scheme' atomic system consists of a standard Λ EIT configuration with an additional level being driven by an additional switch field. We theoretically extend our earlier studies of this model to include a counter-propagating, weak probe field. Using a perturbation method, we first focus on an investigation of the dispersion experienced by the weak probe under a variety of conditions including cold and warm samples, as well as weak and strong switching fields. We find conditions in which the forward propagating probe field experiences normal dispersion while the backward propagating field experiences negative dispersion. We next turn to a similar study of absorption in this system and explore regions of high dispersion with vanishing absorption.

© 2012 Optical Society of America