Sagnac interferometry in a slow-light medium

Abstract

We use a Sagnac interferometer to measure the dispersive and absorptive properties of room temperature Rubidium vapor on the ${D}_{2}$ line at $780.2\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. We apply a pump beam such that the resulting $\ensuremath{\Lambda}$ system exhibits electromagnetically induced transparency. Using a ``biased alignment'' technique we demonstrate a direct and robust method of measuring the rapid variation in the refractive index. Such a ``slow-light'' Sagnac interferometer is ideally suited to precision measurement applications such as magnetometry and inertial sensing.