Refractive Index Enhancement in an Atomic Vapor

We experimentally demonstrate a scheme where a laser beam experiences an index of refraction of 10$^{-5}$ with vanishing absorption in an atomic medium [1]. The essential idea is to excite two Raman resonances with appropriately chosen strong control lasers in a far-off resonant atomic system. We observe this effect by utilizing the hyperfine ground states of $^{85} $Rb and $^{87}$Rb simultaneously in a thin vapor cell heated to 150$^{\circ}$C. [1] N.~A.~Proite, \textit{et.~al.}, Phys.~Rev.~Lett.~\textbf{101}, 147401 (2008).