Behavior of sodium atomic vapor in optical cavities below the threshold for bistability.

Abstract

A study is presented of the transmission characteristics of low-finesse ring and Fabry-Perot optical cavities containing sodium vapor and operated below the threshold for optical bistability. Novel features are observed in the transmission signals obtained as the laser light frequency is swept through resonance with a sodium D transition. The ring cavity transmission peaks display a broad absorption profile except for the peak which is tuned to the center of the profile which is almost completely transmitted. A similarly tuned cavity transmission peak in the Fabry-Perot \'etalon is split into three, with the central peak being very narrow. A theoretical description for each cavity is developed in terms of a \ensuremath{\Lambda}-type, three-state model for the atomic energy levels associated with the transition. Using parameter values based on the experimental conditions, theoretical transmission signals for the linear cavity are obtained which are in good detailed agreement with the experimental results. For the ring cavity, agreement is also good except for the degree of absorption of the central peak.