Refractive index enhancement with vanishing absorption in short, high-density vapor cells

It has recently been predicted and experimentally demonstrated that the refractive index of a vapor may be enhanced while maintaining vanishing absorption by using the interference of two Raman transitions, one absorptive and one amplifying in nature. In this paper, we present a detailed experimental study of this technique in a 1-mm-long rubidium (Rb) vapor cell with densities exceeding 10¹⁴ cm^-3. We study the optimization of the achieved refractive index as various experimental parameters are varied and discuss a number of limitations of the current experiments. We also present a detailed discussion of possible experimental improvements and future prospects of this technique.