Atomic coherence effects within the sodium D1 manifold. I. Creation of coherence and dressed state analysis

The connection and similarity between two different models for lasing without inversion are studied, and various dressed state pictures enlighten its physical origin. Recent experiments on coherence effects in sodium are reviewed. The existence of atomic coherence in these experiments is critically examined. It is found that the hyperfine structure and the coupling coefficients within the sodium D1 manifold are of crucial importance.